I'm also as biased as anything as I used to be CFI at Leading Edge.
I won't get into a who's better slanging match, but I would say that from an instructing point of view having the same FI and using the same type is critical to you doing as well as possible.
The odd change of FI to keep a check on your progress is fine, but to constantly have different FI's just doesn't work.
Oh yeah, don't pay upfront to anyone! Ever...No matter what terms they offer you.