darksiders 2 is a very good game, its like zelda/god of war combo. if u liked the original u will like it just as much.
black ops 2 is very fun
assassins creed 3 is a good game as well
batman is pretty decent

The same is true of AC3 though. The instant fail when detected mission are very annoying when the game decides you're detected in the one split second before a guard dies. And the nonsense instant spawning of groups of guards during fort take overs when a double assasination doesn't work and takes 1.5 seconds is very irritating.
The combat is more rewarding in Batman, in AC3 it feels more like a long qte, almost impossible to lose except out of annoyance at the continual respawing at notoriety level 3. Easier to die and reset instead of taking the trouble to run away and have to come back again.

The naval battles are fun (but short). Exploring and experiencing the world makes it worth it for me. Story and mission were better in Batman.

Go with AC3. Batman games are incredibly overrated.

I'd say Mass Effect 3. Easily the best of the three, great port. From these two, I'd go for Batman.

You should be asking on MiiVerse where you will know if people have actually played the game or not before giving their "authoritative answers"

That aside, I have played both games (AC3 on Wii U; B-AC on PS3 & Wii U) and I think you should choose based on the following

Assassin's Creed 3 - Action / Adventure with weird modern world sections and absolutely awesome historical sections. Really amazing multiplayer mode too but a pain to get working properly on Wii U due to NAT resolution issues they need to patch.

Batman Arkham City Hardened Edition - Stealth / Adventure which is one of the best stealth games and easily the best Batman or Comic-Hero video games made to date.

Now for the inevitable Wii U vs. PS3/X360. AC-3 looks better on Wii U but multiplayer community is minimal and needs some NAT resolution patches. B-AC has too much bloom lighting and poor textures in some areas on Wii U.

Both are good games well worth your time and money

Ninja Gaiden 3 - Razor's Edge | Best 3rd person action game on Wii U (or including PS3 / X360 as well because I think better than Bayonetta and NG2)
Darksiders 2 | Best action adventure fantasy game on Wii U
Call of Duty - Black Ops 2 | Best FPS on Wii U; Also best for Online competitive play on Wii U (because community active 24/7)
Assassin's Creed 3 | Best action adventure realistic game on Wii U
Batman Arkham City Hardened Edition | Best stealth adventure game on Wii U

Aside from purely Shooter fans (CoD is it for you), anybody interested in any one of the others above really should be interested in all of them.

...

I still haven't tried Mass Effect 3, but it has the highest aggregate average review scores of any Wii U game (on Metacritic or GameRankings)

Batman if played as intended is an open ended puzzle game where each scenario is something you have to decide how you will take out all the goons doing only as Batman can... or you can do it the action approach which will probably get tedious and not as satisfying.

AC3 is actually the same way in that most situations there is a way (not open-ended; i.e. one right way) to get through without alerting/fighting any guards and that feels most satisfying, but you can also just go in fight your way through and start to find the combat pretty tedious. The game tries to encourage you to discover the stealth apprach to have 100% synchronization.

Seriously... while Batman forces Stealth more (you die fast if you don't play smart), both the games are very similar while being distinctly different in how you actually play (except melee combat which is same wait for attack, counter, rinse and repeat).

I'm not sure about the Wii U versions, but I think that Arkham City is a vastly superior game to AC3.

AC3 just felt empty and lifeless and low effort, really.

i've been playing through batman and i think it's fantastic. I haven't noticed any frame rate issues at all. I really like the use of the gamepad with it.

I haven't played either of them (on the Wii U at least) but I'd probably say Batman. They changed/added thing just for the Wii U so it might mesh better.