Jake the Cobra (killing throws) is just awesome. And since thrown weapons bounce on the walls you can easily take down several guys.

I have replayed the game with Tony the Tiger (killing punches) and the game is surprisingly easy and fun this way.

Peter (Unicorn), Tony (Tiger), Graham (Rabbit). I haven't tried Phil (Fish) yet, but that one sounds awesome, too. :D

I needed Tony for the bonus level - it seemed surprisingly hard - probably as there's very little cover.

The double swing doors at the entrance are your friend. Great opportunity to play hide and seek. ;)

The Unicorn mask is overpowered. It makes all your gunshots completely silent, so you can pick the enemies one by one from a distance. And with the auto-targeting, you almost never miss. The police station level was a breeze with that mask.

Don Juan (The Horse) or the Owl mask(forgot the name). I always vary between those two.

Tony the Tiger there GGGGRRRRREAT

The usual richard.

But I really enjoy the Grasshopper's drill kill, which is very funny :DD

Don Juan

Personally, my favorite so far is the Snake mask(Jake). Tony is also pretty great.

I tend to always use Zack, the frog mask, unless I'm fighting a boss. He has never let me down, and I've gotten a few ridiculous combos with his help, such as entire floors of the police station.

I'm partial to Ted and Don Juan...

Ted is nice later on when dogs become a pain in the butt...

Don Juan is just good anytime...