Hitmonlee or hitmonchan

It's a matter of opinion. Both are strong physical sweepers (Hitmonchan-105 Hitmonlee-120).

Hitmonchan is slower and has a bit lower attack power, but he has an ability that boosts punches, which helps him out a bunch. He has a more versatile moveset, meaning that he learns much more moves than the other Hitmons. He also has higher physical defense, meaning that he can be somewhat bulky, but low HP makes him average defensively.

Hitmonlee is the more offensive. Very good physical attack and above average speed, but that's about it. His moveset is good, but not as good as Hitmonchan's. His bulk is horrible, however. He will not be taking any physical hits.

Personally, I favor Hitmonchan because: more bulk, more options for moves, and he looks cooler in my opinion.