Let's see. All three are awesome, but only in certain situations. I'll do a brief pros and cons of all three.
Pros
Hitmonchan-
-Gets punching moves powered by ability
-has diverse movepool thanks to elemental punches.
-good attack and special defense, not to mention decent defense.
-Plenty of moves to cover weaknesses.
Hitmonlee-
-Excellent attack, and special defense.
-good speed for sweeping.
-nice moves to cover weaknesses.
-Good special defense.
-hard hitting, powerful moves.
-ability can either increase damage, or prevent paralysis (helping out that nice speed even more)
Hitmontop-
-Great ability to power up weak moves, making them into a threat.
-Nicely distributed stats.
-decent movepool.
-good revenge moves.
Cons-
hitmonchan-
-Has low Hp, which defeats the purpose of high special defense.
-most people will exploit his lower defense and just use physical moves.
-mediocre speed takes away lots of sweeping potential, forcing him to rely on priority moves.
-Only one good ability limits movepool, and makes your pokemon more predictable.
Hitmonlee-
-low defense. (This one applies to all three of them though.)
-Okay, pretty predictable movepool.
-Most power moves have either huge drawbacks or are unreliable (Like stone edge and it's low accuracy.)
Hitmontop-
-Being the most used of the three, he tends to be the most predictable, the technician set is good, but obvious.
-needs stat boosters to hod up against tougher pokemon, but lacks the defenses to set them up.
-decent speed stat makes for mediocre sweeping.
All in all, my personal best choice would be Hitmonlee, due to versatility and all out sweeping.
