HeliAir at Wellesbourne, run by Mike Smith who is reputed to have the most instructional hours in the UK. He teaches PPL(H) as well as Instructor courses.
HeliAir at Denham is run by Quentin Smith and Glenda Wild (CFI).
I haven't heard anything about their other branches, but Wellesbourne and Denham both have excellent reputations.
Good Luck.