Haunter: Lick vs Shadow Claw

Lick has a short duration so like all shorter moves it would be easier to spam attack and stop in time to dodge. And as you point out it does generate energy faster. Lick generates 6 energy/.5 s and Shadow Claw generates 8 energy/.95 s.

I think I would prefer Lick if there was anything to use it against. ... What are you using Haunter against?

Haunter has really low def, that's why it is not really a good prestiger. It does a lot of damage in the short period it survives.

I use my Haunters as one-way-prestigers after mass evolution, same way as ratticates. I don't even mind about the moveset. Just use it, transfer the body afterwards.