To be nitpicky, I'm pretty sure Hyper Beam is Gengar's strongest move, but Sludge Bomb is the strongest that is relevant.
Yeah, just run the one in the OP. It will do you good.
@ NidokingJ:
If you don't accept a rate, then why do you post here? It isn't good and you should listen to Eon about its flaws. You can't ignore advice saying, "Oh this isn't exactly right," and in fact say "sorry, its really good and you are ignorant of its awesomeness." You haven't once explained why it deserves respect. It has flaws too. You are praising the ones who aren't helping you, the ones who say, "really good, 10/10" isn't being helpful, it's not improving it. Second of all, Sucker Punch avec CS is bad, but you WILL Trickeroo it off, so I don't think it's that bad, but just use Crunch. It isn't situational, although it loses its priority, it just fits with CS. 85 Speed is not at all bad, Chandelure has 80 and it's one of the best non-legendary Pokemon in the game. Just voicing my opinion.