Honestly if you have Fog anywhere in your southern Wild Area, I'd go grab a Ralts or Kirlia. If it happens to be a male, you have the option of either Gardevoir or Gallade down the road, depending on what your team needs (looks to be another Special Attacker though, so probably want Gardevoir).
If you are really set on a choice between the 2, though.... Well, Hatterene is the stronger attacker, but she's a Trick Room Pokemon due to her speed. Without Trick Room, she's on the short list for last Pokemon to move. But that also makes her extremely powerful in Trick Room, because she would instead be on the short list for moving first. Orbettle, on the other hand, is a very defensive Pokemon, with some prominent weaknesses (Fire, Dark, Rock, Ghost) and not the best movepool to work with. But it can work very well in Doubles or Triples in a more supportive role, with Dual Screens for example.