Horses don't hate bits. What they don't like is if you put something in their mouth that doesn't fit their mouth, causes pain or discomfort.
First, the horse needs to have his mouth checked by an EQUINE DENTIST. A good one. To absolutely make sure there are no cracked/broken teeth, there's no uneven wear on the teeth with one side being higher than the other, that there's no abcesses, hooks, etc... and to put in a proper bit seat...which so many vets do not.
The dentist should also be able to tell you about the horse's mouth conformation. Is the mouth short, is the tongue fat, does the horse have a low palate...all of these things will determine the kind, size, shape and thickness of the bit you choose.
I start everything in a hollow mouthed eggbutt and then move from there if I have to. Most stay in that bit, a few have to move onto something else depending on any number of circumstances. I switched my most recent horse to a fullcheek french link after almost two years in the eggbutt.
French link anything is usually quite nice as it allows for independent rein aids...a snaffle or straight bit does not allow for that.