For the benefit of any prospective students reading, I disagree with G-EMMA's downside view of learning to fly under ATC and with the very greatest of respect, do not think that a student pilot has enough experience to have a really considered opinion on the relative merits of learning in an ATC environment versus an A/G..
From a PPL with a few hundred hours (relatively inexperienced as these things go), I believe that there are pros and cons in an ATC, AFIS and A/G environment.
Out of the these, I find A/G to be potentially the most challenging at times, with non radio traffic, pilots discretion and a number of other factors that make it (at least for me) potentially volatile and thus requiring higher levels of situational awareness, e.g. aircraft joining by run and breaks.
Under ATC, there is generally more order and the r/t traffic is generally more predictable.
I learned at an ATC field, but my instructor made sure that I got lots of A/G experience and I found this a good balance.
Whichever environment you learn to fly in, you will need to be up to speed with the others and they all have their foibles.