You don't need a visa. When i did my PPL at OBA i just told them i was over on a flying holiday.
I would go for OBA becuase they have just lost a contract with SFT so they should have plenty of planes available.
Watch out for the boss he can be a bit of a tosser. The other good thing about OBA is you get your RT there as well so everyhing is ready to go in the post when you get back.
MJ