It depends on the level of riding you're at. If you're on the begging side, go to the less expensive barn as when you're beginning you just need time in the saddle. If you're becoming intermediate or above, go to the nice one with better trainers.
I would go to the barn with great trainers, even if you can't go as often maybe you could do barn work to get some more lessons. (most barns offer this but not all) But you will become a better rider there/