Hex or Sucker Punch Gengar?

They're roughly the same as each other. Despite the STAB bonus, Sucker Punch still has higher DPS, but Hex has slightly higher energy gain - though Sucker Punch's is still pretty good.

Sucker Punch allows for easier dodging although the slightly higher energy gain from Hex could mean getting enough energy for another Shadow Ball.

I'd say it's just preference really.

My preference is Hex since it's easier to get 2 SB off vs Confusion Zam.

The slower cooldown of Hex means it's much harder to dodge --> alakazam will obliterate you more quickly

Against Confusion Zam definitely go for Hex because you need to build up that energy for 2 Shadow Balls. Against PC I'd just go whichever you prefer personally.