IMHO, the answer is whichever one you feel most comfortable with.
Of the issues you raise, the size of the airfield is completely irelevant. If you train at a big airport like Glasgow, you will need to spend extra time at small grass airfields where you are responsible for looking for traffic and making decisions before you're happy with that type of field. On the other hand, if you train at a small grass airfield, you will need to spend extra time at a big ATC field before you're happy there. Either way, your instruction should contain an element of each of these, so that you are well prepared to go to any field for more experience once you've got your license.
The price difference between the two sounds fairly small - although, without knowing your financial position, I can't really say whether it's too small to be significant. £110/hr for a C152 does sound a little steep, I have to admit.
So, if neither of those two issues is important enough to worry about, then how do you decide between the two? I would suggest that you go to whichever one offers you an instructor who you are most comfortable with - that's probably the single most important factor. There is nothing wrong with having a trial lesson at each field before you make up your mind.
Good luck!
FFF
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