Dante - seriously he's half devil, and with devil trigger what zombie is gonna be able to do much to him, I doubt he'd even be infectable because of the devil blood, and he can take serious damage without being any worse for wear (see DMC4 for an example)
Samus - metal...teeth...just isn't happening, not to mention if it all goes horribly wrong she's got a remote controllable ride to get you out of there...
Geralt - he's a monster hunter, he's a witcher, he's intelligent, he knows what to do.
Oddly enough, none of these are 100% human, but they're not really what you'd call superhuman.
They also have enough specialities between them to cover each other and you. Dante is probably the most rounded, Samus has the most kit and strongest ranged equipment, and Geralt, well, he knows how to get up close and personal and come out breathing, zombies/undead are just another monster to him.
None of them are stupid either, they're smart enough to know when to fall back etc, some of the other obvious characters like Duke and Doomguy are a little too...direct.