Simple answer on both fronts. Nintendo and Data Design Interactive. Brutally obvious, but doesn't really add to the discussion. I'd rather look at it in different categories while disqualifying Nintendo and DDI. I say this as a huge HUGE Nintendo guy but I praise them enough in other places and some deserve recognition.

Most Improved: EA. They went from being pop-shovelware assholes to a publisher willing to take risks and make good games.

Fallen from Grace: Activision and Ubisoft. While both have had their ups, Activision became the devil and Ubi became the godz of pop-shovelware this generation.

Most diverse and good: Sony. As much as I like to rag on them for being shameless rip-off artists in the hardware department, regardless of fanboy affiliation you can't deny their software has been both diverse and excellent. I think that's what bothers me about Sony is when they go their own way and really try to strike out in new territory, it turns out really well. I wish they'd do it a lot more. Too many great games to name, though some stumbles, overall it's been a great experience since I got my PS3.

Least diverse or diverse but bad: Microsoft Game Studios. Shooter shooter shooter shooter then make "casual" games. Meaning "try to be Nintendo but fail fucking utterly in every conceivable way because you think new or less serious gamer means retard". They just don't get what makes Nintendo godlike in this department and it's painfully obvious.

Best indie/unique: Suda51. The dude's a volcano of awesome shooting his hot load all over the face of gaming.

Worst indie/unique: Not sure here, to be honest. Curious what other opinions are on the matter.

Best tech wizards: Shin'en. Awesome games with great graphics under 50mb. They're some freaking geniuses. I could care less what you do with unlimited power (sup Crytek) but I'm very impressed with guys who do amazing things with very little.

Worst tech wizards: Bohemia Interactive. Awesome games, and my favorite (only?) infantry simulator. But they optimize like a drunken chicken pecking at a keyboard.

Not really an opinion question (best and worst publisher), we have sales data and cultural impact that answers both questions pretty decisively, but different categories we can argue about and think about all day.

Best: Sony, Nintendo, NIS, Atlus, and a few others I can't remember.

Worst: Square Enix, Namco Bandai, Activision, EA.

Not sure where MS lands this gen, because I can't really remember what they've published this gen.

Bethesda. I don't understand how a company can release games in such shitty condition over and over.

I am not sure why people are bashing Square Enix. I think they did fairly awesome and are one of the best publishers this generation; there's about 10,000 iOS/Android/Facebook developers and publishers that are easily much worse. I bought (way) more Square Enix games this gen than any other company, and this is the first time that has been the case since the SNES/Gameboy/Genesis era. While some people are criticizing them for remakes, the remakes are fairly heavy, including many new features, gameplay improvements, and new scripts; and personally I think it is awesome that they revised these games for a new generation, taking along what they learned along the way - not to mention, many of these games never saw western releases before, and now we're getting heavily updated and improved versions of them. This generation Square Enix brought:

* Dragon Quest 9 - which ended up being my most played game of all time, I probably played this one more than my next 5 longest playthroughs of games combined.
* The World Ends With You - one of the most unique and refreshing games I played this generation, no other game used the DS better.
* The Zenithia trilogy remake ended up being my favourite games of the generation, and Dragon quest 5's remake is my favourite RPG of all time.
* Final Fantasy Tactics A2 and The Lion War - ended up being surprisingly great games, one a remake with a much improved script.
* Final Fantasy IV DS was again, an excellently executed remake, it was more or less playing a great version of a classic game; and playing it all over again for the first time. Fixing all of the flaws of the original, and improving on it with a much improved and enriched script.
* Final Fantasy 4 AY - is the game I wanted to play as a kid, better late than never at all; It was a longer story than the original FF4, and the characters were improved significantly (particularly Palom and Porom); and the new characters were very interesting and likable.
* The Final Fantasy 7 spinoffs on PSP
* Crystal Chronicles series (I really liked Rings of Fate and feel that Crystal Bearers is one of the most underrated games of the generation)
* Dissidia
* Tactics Ogre Let Us Cling Together is a fantastic re-imagining as well.
* Chrono Trigger had some good and not so great stuff included, but it was nice to see it appear on a handheld, finally.
* Square Enix also finally released Final Fantasy 3j in the west, and an updated version of the game; this was one of my favourite RPGs on the NES (probably next to DQ4 only) and was very happy to play through with my monk team =)
* Kingdom Hearts games (I haven't got around to these ones yet).


And no, it is not some Eidos game I am looking forward to from them; Square Enix took over Eidos to expand their market to the type of gamers who are into games like Kane and Lynch, and Tomb Raider - I am interested in Dragon Quest X more than any other game.

Final Fantasy 13 turned out to be disappointing due to missing features that were present in most other FF games; but the game itself is still perhaps the best looking game on PS3, and easily the best RPG on PS3 or Xbox 360; although, home console RPGs weren't very good this gen unless you are into PC-style RPGs - which are a bit of a different genre; the great RPGs were mostly on handheld.

Not to mention, Square Enix has purchased some older companies who had collapsed, and has breathed life back into them; Eidos being the major one.

Of the major publishers, the biggest loser this generation was easily THQ. I can see them being bought out soon. THQ has been constantly shrinking as a company, losing ground. 

Biggest fall from last gen was Sony; Sony went from first to third, and sales of the PS3 are nearly 100 million down from last generation's PS2. 

Biggest improvement from last gen was Nintendo. Nintendo more than quadrupled sales of their home console over last generation, and doubled handheld system sales over last generation. They also managed to be WAY in first for software sold on their two consoles with software numbering over 1.35 billion this gen.

Best - Square-Enix (yes suck it haterz)

FFXIII, Just Cause 2 -- Among my fav console games and Just Cause 2 totally made up for GTA4 sucking

SO4, Nier -- Two console games I enjoyed very much

KH:BBS, DQIX, TWEWY, FF7:Crisis Core, Dissidia 012 - Fav portable games this gen

FF Tactics A2 - A enjoyable portable game

Chaos Rings - The BEST itouch game I have played

DQV, FFIV - Fav Remakes this gen

So overall no other publisher has given me such breadth of quality this generation with only 2 major disappointments (if only The 3rd Birthday didn't suck.....and of course FFXIV). They have shown such great imporvement from the PS2 generation, I hope it continues!

Worst - Namco-Bandai

Where are your Tales games? They all look so great but where are they? If Atelier stuff can be localized there is no excuse not to localize Tales.

Most Surprising - SONY

They completely got everything together after PS3's sales fall and pumped out quality after quality coming on to even rivaling Nintendo. No-one could have imagined such great titles would be coming out from them.

Most Disappointing - THQ

Not many Tycoon games this gen, why?! (at least not the ones I want)

Most Efficient - Sony

Thanks to 2 year dev cycles they get many titles out in 2 years flat and they are of great quality.

Least Efficient - Square-Enix

FF Versus XIII is a development disaster (like XIV, XIII and XII before it), it will be interesting to see what went wrong in that project (no project takes so long unless its a development disaster).

FF Type-0 has taken 5 years to come out, its a portable game. FF7 Crisis Core took around 3.5 years to make. The 3rd Birthday took 3 years or so. FFXIV and FFXIII were 5 years in the making and the crystal tools engine which ate up most of FFXIII's dev time is now an engine thats already being replaced by luminous...so making that engine was a complete waste of time.

I really don't need to say more to prove how inefficient they are.

@ Paragraph 1 - I agree, they are clearly not the worst. I voted them the biggest deterioration and I stand by it.

@ Paragraph 2 - Publishing takes no skill, developing takes skill. DQIX is one of the reasons Level5 got mot improved. S-E do not get credit for it.

@ Paragraph 3 +1

The best is easily IMO Nintendo, quality is of course subjective, but it is hard to deny it from a sales/influence/etc point of view.

I'm not sure about the worst, but the most dispointing IMO would easily be Square-Enix. Actually, Namco-Bandai would probably be the worst with their God awful handling of the Tales series.

I MUST apologize to THQ, they are not my most disappointing publisher, Tycoon games are among my fav genre

but

The most disappointing publisher is Lucasarts

I cannot believe how mishandled STAR WARS has been this generation.

Not to mention Capcom basically stole their point n click adventure games dominance with Phoenix Wright series and this years premiere title, Ghost Trick.....Atlus also conquered with 999.

But forget everything else, they have Star Wars, the most powerful IP in the world and they haven't done anything that good with it this gen. The Wii was basically made for a star wars light saber game, no battlefront 3, no empire at war sequel (star wars RTS game), no jedi knight series continuation, no jedi academy series continuation, no tie fighter, no pod racing game. Just lego...but lego star wars started last gen and the force unleashed games which could be better.

KOTOR/KOTOR 2 proved last gen that a "good" star wars game can be among the best games ever, we don't even have a sequel to that.

Just random fact. Dragon Quest/Warrior was never made by enix either, they've been developed by Chunsoft, Heartbeat, ArtePiazza, Armor Project,and level-five. 

And if I recall correctly. Enix Was just a publishing house. So they get no credit for anything then. :P

Blizzard does the best every generation. On consoles, probably Naughty Dog if we talking quality. But sucker punch is my favorite.