Hydreigon is unfavorable with his 4x weakness to fairy. It's a tough choice between the other 3. Salamence has the most well rounded offensive stats, garchomp has the best coverage for fairies out of the group (poison jab), and Haxorus can destroy things with his high attack. So it comes down to this: do you want coverage for fairies, or do you want a slightly more potent offensive force. I would choose Garchomp because though his offensive stats aren't as good, he's still really powerful and he can use poison jab to check fairies while Haxorus has nothing really while salamence has the pathetic Steel wing, but the other Pokemon are still good.