Which is a better dark charge move on Houndoom for pvp?

Foul Play. ETA: Even with Ttar stats and a quick succession of hits, Crunch isn't strong enough to deal neutral damage if caught out by a switch or faint.

Cacturne is doing for me nicely, as is Crawdaunt. I have Cacturne with grass quick and dark charge and Crawdaunt with dark quick and water charge. I also use a SD/C Tyranitar. (Different teams, different coverages. All are on teams with a 75%+ win rate over at least 12-15 battles each)

Shiftry I found, oddly, to come off less bulky than Cacturne despite better defensive stats and identical typing. I haven't tried Honchkrow despite having a perfect or Weavile.

Umbreon is still pretty solid in ultra league, but needs to be up at level 35+... Alolan Muk is also solid with dark pulse. It's poison resistances completely neutralize its dark weaknesses, so it ends up being weak only to ground. I like to pair it with poison jab instead of bite since it gains energy nearly twice as fast so you'll launch a lot more charge moves.

Umbreon and Muk-A should both be much better dark types than Houndoom, Umbreon needs to be very high level though. You want TDO, not DPS, and Houndoom isn't exactly tanky.

It's also a relevant question to ask what you're using the dark types against. For Cresselia, a steel-type is much better, because Cresselia can't murder it with Moonblast like it does to dark-types.