Infernape is arguably the best of the starters' evolutions due to its solid attacking ability and diverse movepool. When combined with a Life Orb, it can wreak havoc on opposing teams. Plus, the Chimchar line represents the only fire types in the D/P Dex other than Ponyta and Rapidash. This makes Chimchar even more desirable.
Infernape's Base Stats:
HP - 76
ATK - 104
DEF - 71
SP ATK - 104
SP DEF - 71
SPEED - 108
Weak to - Water, Ground, Flying, Psychic
Resistant to - Fire, Grass, Ice, Dark, Steel
Very Resistant to - Bug
Neutral to - Normal, Electric, Fighting, Poison, Rock, Ghost, Dragon
Torterra's Base Stats:
HP - 95
ATK - 109
DEF - 105
SP ATK - 75
SP DEF - 85
SPEED - 56
Weak to - Fire, Flying, Bug
Very weak to - Ice
Resistant to - Ground, Rock
Immune to - Electric
Neutral to - Normal, Water, Grass, Fighting, Poison, Psychic, Ghost, Dragon, Dark, Steel
Empoleon's Base Stats:
HP - 84
ATK - 86
DEF - 88
SP ATK - 111
SP DEF - 101
SPEED - 60
Weak to - Electric, Fighting, Ground
Resistant to - Normal, Water, Flying, Psychic, Bug, Rock, Ghost, Dragon, Dark
Very resistant to - Ice, Steel
Immune to - Poison
Neutral to - Fire, Grass
Everyone can use this to refer to and draw their own conclusions. To me, Empoleon is the best out of them. Give him Ice Beam which takes advantage of that special attack, and he kills Torterra in one hit for sure (and he has more speed to go first). If he can survive Close Combat from Infernape he'll Hydro Pump him to death in one hit, or maybe even Surf. Plus, all those resistances (more than any other pokemon I'm pretty sure?) make him so freakin useful.
Just my interpretation though.