Drapion is better than Spiritomb, but as a Dark-type Scrafty is your best option.
Firstly, Spiritomb isn't available that early or without much effort. You have to be in the post-game to trade one with Curtis/Yancy, or it requires transferring from Dream Radar. Meanwhile, Skorupi can easily be obtained in the late game at Reversal Mountain and it evolves quickly into a Drapion. Note that it's only really useful verus Shauntal, Caitlin and Marlon's Jellicent and not that great rest of the game.
Name: Skorupi
Availability: Late Game, Reversal Mountain, 30% (Outside)
Stats: Good. It's fairly fast, has solid defenses, and a decent attack stat. Nothing exceptional, though.
Typing: Skorupi is Poison/Bug, but shortly after you catch it, it will evolve into Drapion, which is Poison/Dark type. Poison/Dark is a good defensive typing with decent offensive presence.
Movepool: Fairly shallow. It gets nice STAB moves in Crunch and Cross Poison. It also learns the elemental fangs, but those are fairly weak, and its only other usable moves are X-scissor and Dig.
Major Battles: As a Dark-type, it fares well against Shauntal, Caitlin, and Marlon's Jellicent. Because of it's poor coverage, however, it doesn't do particularly well against any other important trainers.
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Scrafty is notably the best Dark-type option you can go for. It gets the elemental punches via the tutor, good moves like Hi Jump Kick and Crunch as early as before evolving into Scrafty. Solo-ing Caitlin, Shauntal and Grimsley of the Elite Four, even not including Ghetsis, Colress, Zinzolin, etc. combined with early availability makes it better than the above two.
Here's a moveset for both Drapion and Scrafty if you wished to use the former as well:
Drapion @ Black Glasses
Ability: Sniper
- Cross Poison
- Crunch
- Dig / Earthquake
- False Swipe / Strength / Cut (filler)
Scrafty @ Black Glasses
Ability: Moxie
- High Jump Kick
- Crunch
- Dig (for Elesa) --> Ice Punch
- Rock Tomb / Strength (filler / HM / coverage)
Hope this helps.
