Which Sneasel should I evolve/power up?

Check out breakpoint calculators to see for your self. They're pretty much identical. Especially for Cresselia raids the attack IV means you hit the breakpoint half a level earlier with your second sneasel (only if you are raiding with a friendship boost though) and the extra HP means surviving one more psycho cut (it might or might not survive and extra confusion)

I'd go for the second one cause I personally don't care a lot about the HP IVs. Close call though. You can't really make a wrong choice

Personally I would make the best team I could with what I already have.... Cresselia isnt worth investing any resources in.... Not dust, TM’s and certainly not an evolution item.... Raid it early, raid with trash, get the Dex entry and move on to raiding more useful Pokémon .... That’s my game plan at least

There are a lot of alternatives to Weavile if you want to use your stone on someone else. Just use your Mewtwo team.

1% more DPS than Tyranitar.

I would power it up only If you like it.