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Volvesta takes forever to evolve, and it barely learns any moves.
I'd go with Scolipede for sure. It doesn't take nearly as long to level up and has a fairly diverse move pool, along with good speed and attack.
Anorith is fun too, but doesn't evolve til later.
Maybe go with shedinja. I've never tried to run one of those on a normal play through, and I bet it'd be really useful. Many mons can't hit it.