The States generally have much more stable weather than here. Possibly; can't advise you on that, all my time instructing was spent in the UK.
Without being familiar with either Derek or the other school, no idea. You'll have to pick. Having said that, I suspect there is no "magic bullet" that DD possess, and others do not.
Any flying school you go to with a half completed PPL will and should want to know your backstory. They won't be able to truly make an estimate of how long you'll need until they fly with you; and even then it'll only be a guess.