Preferred moveset for Crobat

My feeling is that Crobat's strength is that he is doubly resistant to Fight, Bug, and Grass, so why not take attacks that do the most damage to those types (Flying). My fav is Air Slash/Air Cutter - even though it's not as strong in pure DPS, it plays well against those three types and has STAB. Sludge Bomb is only strong against Grass (and has STAB), and Shadow Ball is strong against Ghost and Psychic, while Crobat is weak to Psychic. CDPS is about equal for all three against Fight and Bug (Shadow Ball has a slight edge), while Sludge Bomb is better against Grass. Given that, I'd go Sludge Bomb for a strong dedicated grass assassin, or Shadow Ball to take on Fight and Bug as well as Grass.

Shadow Ball is unlikely to get a type advantage because you are not going to be wanting to use Crobat against Psychic types and people don't usually place ghost types in gyms.

Sludge Bomb with STAB is almost as much neutral damage as Shadow Ball, but it is a lot faster.

I wish Air Cutter was a bit stronger because Crobat could almost be a good fun choice against Machamp.

Yea i know great move set for Crobat. Its called Grow Up and stop using Crobat

AS+SB. SB is not only strong to grass, also to fairy. You said you like fun to play so I think different type of move (both with STAB) will be fun.