Competitively speaking, Heracross demolish Hitmonlee.
Heracross is one, if not the one, best Fighting type in UU and for very good reason.
It's completely unique STAB in Fighting and Bug is excellent offensively (with moves like Megahorn and Close Combat), and it's plethora of other attacking moves (Knock Off, Earthquake, Stone Edge) means Heracross have near perfect coverage. This in turn is backed by an Attack stat of 125 and a perfectly sufficient Speed of 85. It's greatest strength however, is its Abilities. Swarm may be more or less useless but Moxie is amazing and Guts is just godsend. Moxie makes it a terrific late game sweeper whilst Guts transform it into a one man wall breaker army. Usually these abilities work best with the Choice items, either as a sweeper with a Scarf or a wall breaker with a Band. Generally speaking though Guts is more about seizing the day and then switch in as often as possible to land nuclear hits whilst Moxie is more suitable for late game sweeping.
That being said Heracross is more than capable of running other sets as well. It's Mega Stone allow it to run a completely unique set in its Mega Form (which may not be as proficient as normal Heracross but is nevertheless a different, usable set) Substitute+Focus Punch hits tremendously hard whilst a Sword Dance set can demolish most things to slow or to dumb to run away.
There we see Hera's biggest flaw however, it's Speed. 85 is respectable but unless you are running a Scarf set you will fall pray to faster sweepers. That being said most things slower than Hera are more or less dead meat. It is also important to note that there are a few Pokemon that counters Hera, foremost of these Gligar, Gliscor and Hippowdon.
It is however important to note that these three counters almost all Fighters types. Including Hitmonlee which I will now cover.
Right of the bat Hitmonlee lacks Hera's Bug typing and STAB, and although it have more coverage in Blaze Kick and Poison Jab it fails to have the same impact as Hera's unique STAB. Statewise they are near the same although the Lee have less Attack (by 5), more Speed (by 2) and more dedicated defences (more focus on SpDef). Such a minuscule difference shouldn't impact performance that much, but it really do. 87 over 85 Speed utterly fails to make a difference as both are to slow to be considered great, whilst the 5 difference in Attack actually do make Hera hit considerably harder. Defences make little difference, although Lee is much more prone to Priority moves, something it's Unburden strategy is already weak to.
There is also a vast leap in terms of Ability between Lee and Hera. Whilst Hera's serve very different purposes but are both equally deadly Lee's lack that basic versatility. Limber should never really be used due to Reckless and Unburden being better, but these two are very similar. Unburden's biggest flaw is its short duration. It works once per match and most likely less than that as Knock Off is everywhere these days and many teams have walls to handle faster than average sweepers. Reckless on the other, albeit far more reliable, always have to rely on Items to function properly. Despite this it is never quite great. Without a Scarf it lacks the Speed to sweep, but without a Band it can't break walls effectively. As such Reckless Lee will never work optimally, whilst Unburden only occasionally work at peak performance.
Overall the main difference between Hera's and Lee's is their versatility. With Heracross you never know what to expect, both in terms of Ability and set, and something that can counter one set can get demolished by others (An example of this is Sableye, who's Prankster+Will O Wisp destroys Moxie Hera and Mega Hera get demolished in turn by Guts Hera). Despite a relatively small rooster of moves and abilities Heracross manage to be dangerous regardless of set but also equally good at all things. Hitmonlee on the other hand have two tricks, two very similar strategies that more or less is countered by the exact same thing. Unburden is literally a one trick pony, working exactly once per match under the very best of circumstances. Whilst the myriad of Heracross sets have a myriad of opportunities to switch in and start wrecking the place, Unburden Hitmonlee have few places to switch in, if any. It is much easier to counter as a good physical wall of any proves will either be able to hit back with sufficient damage or stall it out. And the very same strategy defeat Lee's Reckless strategy. Wall or outspeed, cripple it a little, regardless of Lee's set it will be walked by the same things.
Certainly both Hera and Lee will be walked by the big three I mentioned earlier, Gligar, Gliscor and Hippowdon, but it is every other Pokemon Heracross manage to deal with better. So competitively speaking, Heracross is the better pick.
A few good sets for both would be:
Heracross @ Choice Scarf
Ability: Moxie
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Megahorn
- Knock Off
- Close Combat
- Stone Edge
Heracross @ Choice Band
Ability: Guts
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Megahorn
- Knock Off
- Close Combat
- Stone Edge
Heracross @ Heracronite
Ability: Guts
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Pin Missile
- Bullet Seed
- Close Combat
- Rock Blast
Heracross @ Leftovers
Ability: Guts
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Substitute
- Focus Punch
- Knock Off
- Megahorn
Heracross @ Leftovers
Ability: Guts
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Swords Dance
- Knock Off
- Megahorn
- Close Combat
Hitmonlee @ Normal Gem
Ability: Unburden
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Fake Out
- High Jump Kick
- Knock Off
- Poison Jab
Hitmonlee @ Choice Scarf
Ability: Reckless
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- High Jump Kick
- Poison Jab
- Knock Off
- Stone Edge
Source: Experience with Heracross in both gen 5-6, an a good understanding of Heracross strengths and weaknesses.
