Is this a Walking Dead only thread (the OP seems to suggest it, though the title is more broad in the candidacy).
I'm going to go with Handsome Jack from Borderlands 2.
I've also enjoyed Cortana, much more than I have in previous games.
Cortana was great,although i was a little embarrassed* at how much more naked she looked(didn't put me off her though),sure she has been naked in them all,but her T+A were much more evident in Halo 4,and that's where my eyes were drawn to everytime ...felt kind of wrong,with knowing her in the past games
she is still a great character,and more so in Halo 4
*is the word i will use
Overall,Jack and Tina from Borderlands 2
would be high,if not the top of my list,Tiny Tina wasn't in it for that long(i heard she was in the new DLC,is she?),but Jack kept me laughing all the way through the game,him and Butt Stallion
Honourable mention for great game character = Captain Rast Brattingan
from the Kingdom of Amalur:Reckoning DLC>>The Legend of Dead Kel
I loved her,she was funny,flirty and a little bit ditsy
I am going to throw this in the ring,worse Character would be James Vega
from Mass Effect 3..he did nothing for the game IMO(EDI and even Javik the Protheon were better),I don't really like bringing up ME3 when it comes to 'the worse off',because it still hurts what that game became(could of been great,missed opportunity etc etc),.....that game cut the deepest when it came to disappointments this year