There is no "better" one, but I will give the pros and cons of both
You said this is in black, the two fossil Pokemon I am assuming you are meaning are carracosta and archeops.
It is a very good sweeper, and can take out a lot of Pokemon ingame.
It has a decent movepool and pretty good typing, dragon claw helps a lot in gen 5 (no fairy).
It's ability is very bad.
It's typing is meh.
It can't take very many hits, it hits first and hits hard.
Archeops @ Focus Sash
EVs: 252 Atk / 252 Spe/ 4 HP
- Stealth Rock
- Head Smash
It can take 2-3 attacks.
It has a much better ability (abilities)
It's typing is improved with Solid Rock
It makes a decent HM slave.
It has access to aqua jet.
It has lower stats than archeops.
It has a x4 (x3 with solid rock) weakness to grass.
It is slow.
Carracosta @ Leftovers
Ability: Solid Rock
EV's: 4 HP / 252 Att / 252 Def
Hope this Helps you choose!