Having trained with both large and small training organisations and airfields, I much perfer the smaller opperators.
Smaller ogrganisations usually allow for more flexible flight sceduling, most of the instructors I have come accross are very experienced and are there because they enjoy instructing and not focused on building hours.
The only real downside is the aircraft are usually older.
You will probably make quite a saving with airways and landing fees as well at a smaller field.
Up side of training at a larger airfield is getting used to flying in cogested airspace this can be very scary if your not used to it.
Alot of flying time can be wasted trying to find a free piece of sky in which to practice training menouvours in congested airspace.
To sum up, Stick to the smaller fields/organisation but make sure you get plenty of practice flying in busy airspace if you can
good luck
