The claw fossil holds anorith, which evolves into Armaldo at level 40. Armaldo is more of a speed/attack pokemon but, a downfall to this pokemon is that its type is rock/bug, so it has many weaknesses.
The root fossil hold Lileep, which evolves into Cradily at level 40. Cradily is more of a defence type of pokemon. This pokemons type is rock/grass. since there isnt that many amazing grass types in Sapphire(other then bellosom,Sceptile, and vileplume) this would also be a considerable choice.
The main basis for whichever one you pick is entirely up to your battle style. You should base it off of your team, Armaldo is a sweeper and Cradily is an annoyer/possible tank.
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If given to the Devon researcher in the Devon corporation the claw fossil can be revived into Anorith.
To get a Lileep in Pokemon Ruby, Sapphire and Emerald you need to revive a Root Fossil. The Root Fossil can be found on Route 111 however choosing it will cost you the ability to get the Claw Fossil. Alternatively you can trade for a Lileep from another game if you've picked the Claw Fossil.
Anorith
The Claw fossil is a fossil which contains a Pokemon named Anorith, for you to get Anorith is to take the fossil and give it to a scientist in Devon Corp. (Rustboro City). After some time he will call you and tell you to come for the Pokemon (Anorith).
You get it by getting a life...and not playing Pokemon...