I guess I'll answer.
Venomoth: 70 / 65 / 60 / 90 / 75 / 90 BST: 450
Butterfree: 60 / 45 / 50 / 80 / 80 / 70 BST: 385
Beautifly: 60 / 70 / 50 / 90 / 50 / 65 BST: 385
Mothim: 70 / 94 / 50 / 94 / 50 / 66 BST: 425
Dustox: 60 / 50 / 70 / 50 / 90 / 65 BST: 385
Venomoth wins. Obviously. Based on BST and SAtk and Speed stats.
Venomoth: Shield Dust / Tinted Lens / Wonder Skin
Butterfree: Compoundeyes / Tinted Lens
Beautifly: Swarm / Rivalry
Mothim: Swarm / Tinted Lens
Dustox: Shield Dust / Compoundeyes
Losers: Beautifly and Dustox, as they do not have access to Tinted Lens, which is arguably the best ability for the bunch.
Well, in terms of tier placement, Venomoth tops all, being in BL2 while all the other bugs reside in NU.
Venomoth: Quiver Dance, Baton Pass, Bug Buzz, Hidden Power, Sludge Bomb, Giga Drain, Roost, Energy Ball, Morning Sun, Psychic, Sleep Powder, Toxic Spikes
Butterfree: Sleep Powder, Quiver Dance, Bug Buzz, Hidden Power, Giga Drain, Psychic
Beautifly: Quiver Dance, Bug Buzz, Psychic, Hidden Power, Shadow Ball, Giga Drain, Morning Sun
Mothim: Quiver Dance, Bug Buzz, Energy Ball, Psychic, Hidden Power, Shadow Ball
Dustox: Quiver Dance, Bug Buzz, Hidden Power, Sludge Bomb, Moonlight, Psychic, Shadow Ball
Venomoth wins, as it has a decent sweeping movepool, as well as access to Baton Pass and Sleep Powder.
1. Venomoth. Not only can it sweep with Quiver Dance, it also has Baton Pass, allowing it to create monsters.
2. Butterfree. It has both decent SAtk and access to Sleep Powder, facilitating its sweep.
3. Beautifly. It does have access to a large range of coverage moves, but will often need to resort to Focus Sash for longevity. Also has good SAtk and okay Speed.
4. Mothim. It has good SAtk and lame Speed, but it outclasses Dustox in both.
5. Dustox. This guy sucks. Poor Speed and SAtk, and can get revenged easily due to its poor Speed.