A mono poison team huh? Alright lets compare.
Skuntank: poison/dark
HP 103
316 - 410
ATTACK 93
171 - 313
DEFENSE 67
125 - 256
SP. ATK 71
132 - 265
SP. DEF 61
114 - 243
SPEED 84
155 - 293
TOTAL 479
Weaknesses: ground
Resistances: ghost dark poison grass
Immunities: psychic
Notable moves: sucker punch, crunch, pursuit, flamethrower, haze, momento, roar, fire blast taunt, sludge bomb
Scolipede:bug/poison
HP 60
230 - 324
ATTACK 90
166 - 306
DEFENSE 89
164 - 304
SP. ATK 55
103 - 229
SP. DEF 69
128 - 260
SPEED 112
206 - 355
TOTAL 475
Weaknesses: flying rock fire psychic
Resistances: fighting(double), grass(double), bug, poison
Immunities: none
Notable moves: spikes, toxic spikes, megahorn, poison jab, aqua tail, rock slide, superpower, earthquake, superpower, swords dance baton pass pursuit
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Time to compare
Defensively, skuntank is the superior. It gives you a crucial psychic immunity. It's sole weakness to ground can be easily handled with partners like Crobat, weezing, and amoongus. It has great utility moves like taunt and haze but other wise it's movepool is lacking. With no decent physical movepool outside of his stabs, he most run special fire attacks and hidden power for coverage. However what little movepool it has still gives it an important niche. It's STAB pursuit guarantees the death of opposing psychic types. He also has STAB priority sucker punch, meaning that he can kill most opponents before they move. In the end, Skuntank should be used as a utility Pokemon with offensive prescence. However, Drapion gives it stiff competition in the role.
Scolipede, although rather poor defensively, is an offensive monster with its STAB megahorn. It's base 112 speed allows it to outspeed much if the metagame, most notably the lati twins, with megahorn, pursuit, aqua tail and earthquake, scolipede can effectively check all the threats that burden your poison team, namely psychic, ground and steel. Add the fact that it can be a utility Pokemon with substitute, swords dance, baton pass, toxic spikes and spikes, it would seem that scolipede is a great choice, and indeed it is. Basically, choose Scolipede
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Here's a personal favorite set
Scolipede@black sludge
Nature: jolly
Evs: 4 hp 252 atk 252 spd
Ability: swarm
Substitute
Swords dance
Megahorn
Baton pass/aqua tail
Long answer I know but hope this helped.