Nintendo 

Pros:

Amazing Games

Amazing Console

Games actually work on launch

Cheapest console

Cons:

NOTHING!

Extremely unbiased, I must say!

Honestly it would be hard finding three things I like about all three. So I'll just start by putting my strongest foot forward.

SONY

+ Diverse library, they basically have a very very good game in every genre out there. Something for everyone and they support games that otherwise would never have seen the light of day. 

+ The maintain a very open platform. Basically allowing devs do anything devs want to do, cross platform play? go right ahead. 

+ They do not bleed their IPs to death, you can pretty much guarantee that with every Sony platform, their will be a slew of new IPs, for better or for worse.

- Slow feature updates. Makes you wonder what they spend all their time doing. 

- They have a habit of doing last minute marketing for their IPs, not allowing the games get as much exposure as they could. 

- did I ,mention slow firmware feature additions? 

MICROSOFT

+ they know how to market their games. They can make any game seem like the biggest and best thing that ever happened to gaming, and the media eats it up. 

+ They made the whole concept of a networked connected console a reality.... for better or for worse. 

- At their core, they do not really care about gamers or the industry. if MS had free reign over the industry, it would be a very very very sad day for gamers, everyday. They would suck us dry.

- Very poor first party support. They tend to have only one major game release per year. 

NINTENDO

Drawing blanks here... Only thing I can think of that's what saying is that they make some great first party "nintendoish" games. won't list out their negatives cause well, it could just be like their positives; a very nintendoish list of negatives. 

I'm moderately biased towards Sony and Nintendo, I believe. I really don't like MS that much but at least I tried to! :P

im a fan of Sony but not a fanboy who cant recognize when they have fucked up, that being said as for the other two... they do have one game here and there that looks good but they fail to satisfy my gaming needs as much as Playstation does.

for example:

i love both Japanese and Western games and Playstation gives my a LOT of both (heck the PS3 is still getting japanese exclusives), and i also love new IPs and Sony has always been really focused on that as well.

Now if we look at Xbox they focus totally on big AAA western games and they have an almost complete lack of Japanese games.

Then we have Nintendo which has mainly the IPs and games that i either stoped caring after i grew up (like mario) or i never actually cared about before and now (like Starfox, Donkey Kong), that being said they DO have some games that im interested on their system but as of right now its just three games (Bayo 2, W101 and Xenoblade 2), plus if we add the fact that they lack Western exclusive games (like Uncharted, Halo, GOW, Infamous, TLOU etc) and the fact that they lack third party support then they dont even come close to filling my gaming needs...

and thats why i game on a Playstation.

PS: i also never Troll/Flamebait/provoque and or downplay the awesome stuff the other consoles do have, and i hate fanboys even the ones on PS side, because they end up making us look bad...

I'll admit I have like a 10% bias for Sony but i've always purchased all consoles. I really don't like being stuck behind once machine.

Pros: Too many games to buy!

Cons: Not enough money!

I can't explain to you why I am unbiased without being biased.

I just realized how stupid that sounds.

Being unbiased is almost impossible. Everyone`s got their bias on certain things, just more so than others : P

I'm too lazy to fill out all of that, but I'm pretty confident that I'm unbiased. I don't downplay a company's strengths just because I don't like them, and I don't praise something just for being by a company either, and I think both of those things are pretty much at the heart of the matter. If a game is fun, I'll play it. If it's fun but I don't want to support who made it, I won't play it, but I won't pretend like I never cared about it anyway. Hell, I consider myself a Nintendo fan more than anything, and I think they're devolving into the biggest puddle of crap right now. I'm not going to defend their bad decisions because I like them.

So yeah, I'm pretty confident that I'm not biased. Just extremely opinionated. XD

I'm extremely biased towards Nintendo but I'm not a fanboy, I can see their flaws and when they fuck up, (which has been a lot in recent years). I'm also pretty critical when it comes to them, more so than with Sony and MS.

I'm only moderately biased towards Sony.

With MS I don't really care.

Regardless of my biases I want all companies in the gaming world to succeed so we can all play the games that we love.

Oh and OP, I feel that your list is pretty much spot on.

I try to stay unbias console wise. I defend Nintendo/PS/XB/PC when I have to and try to keep an open mind.

I am, however, very bias against Final Fantasy/Zelda/Pokemon fanboys as I feel they are too negative compared to other series fanbases and it annoys the absolute shit out of me to hear them bash each other so I hate 99% of them v.v
but yes, I try to stay open minded towards all sorts of gamers despite being a Sony/Nintendo handheld gamer for the most part