I'd go for the comedy ones - 'Shaun of the Dead', and 'Zombieland'. For the more serious ones, I don't know.. George Romero's ones, probably - though, apparently, his most recent ones aren't all that great. Or, 'The Walking Dead' series... that's pretty good, from what I've seen (though, it's not a movie... obviously)
You can usually divide zombie movies roughly up into the ones that focus on the characters, and the ones that focus on just showing people being killed by zombies - with the ones that focus on the characters being better, by far. Though, honestly, even the good ones all start to look the same after a while.