If you learn at a small airfield you should not have much difficultly going to larger airports when you have your PPL, IF you are properly trained. I venture the opinion that (some) pilots trained at big fields with ATC have more difficulty dealing with small a/g or non radio fields than do (some of) their counterparts who trained at the small fields. Learning to land, to do balanced turns, to navigate: that sort of stuff is the tricky bit in a flying course. Learning to use the radio and deal with ATC etc is easy.
Two suggested answers to the question:-
(1) It doesn't matter: go to the place where the school gives you the best vibes in terms of instructor attitude, aircraft maintenance, general friendliness etc.. This might be at Little Windsock in the Wold, or at Megaburg Intergalactic Spaceport. Doesn't matter.
(2) An individual choice might depend upon your future aspirations in flying. Do you wish to go professional? Do you wish to get into fast touring, IMC etc? Do you prefer grass-roots flying (grass roots usually means grass strip, but not invariably: North Weald is a grass roots sort of place, but has great big concrete runways all over the place). If flying is to be a hobby, what sort of experience and ambience are you looking for? If you are thinking of a career, perhaps the counter-intuitive approach of going for the small field is good, as when you are a 747 Captain you will (fondly?) remember and understand the base of the industry's structure, and maybe still play a part in it.
There is no right or wrong answer. I would say: choose the school before the airfield, and have fun in your course.