It all depends on what you're using them for. Hitmonlee and Hitmonchan can both run very nice offensive sets in a competitive battle, but they don't go far in the way of defense, even though special defense is a higher stat. Both have fairly low defense and a Scizor with Technician/Aerical Ace could most likely easily wipe out these two. Hitmontop can be either defensive OR offensive, or kind of a "anti-attacker", knowing moves to deal out heavy damage while still being able to withstand attacks.
I also want to note the abilities of the Pokemon. Hitmonlee has Limber and Reckless, both of which being almost next to useless in a competitive battle, especially since Hitmonlee learns 0 recoil moves (someone correct me if I'm wrong on that). Hitmonchan, however, runs a VERY nice ability, Iron Fist. Many people have some kind of 'punch move on a Hitmonchan, usually Thunderpunch to deal with flying types. This can deal out some major damage, especially if you've properly EV trained a Hitmonchan for attack. Hitmontop can have either Itimidate or Technician, the better of the two being Technician. This can be very effective when running a Bullet Punch/Mach Punch set.
To wrap up:
- Hitmonlee: most speed and attack of the three; crappy abilities (in my opinion)
- Hitmonchan: most defense of the two; a REALLY effective ability
- Hitmontop: a very good all around Pokemon; fairly good ability, could definitely work to your advantage.
I can't really answer your question if you should keep raising that particular Pokemon or choose another; that is solely up to you. I can, however, help you in any way possible make your decision. So I hope this helps!
*EDIT- as MeloettaMelody pointed out in the comments Hitmonlee's High Jump Kick CAN be powered up with Reckless. I overlooked this at first since it was Crash Damage not Recoil, however both types of moves are powered up.~