Hi,
I did my PPL at AAA earlier this year. Enjoy it! :-)
Re the choice of airplane: AAA indeed only has (or had at the time, at least) one Piper. While I was there, there was only one student learning on the Piper - and mind you, he went home without a PPL but with tears in his eyes because the Piper was on unscheduled maintenance for the last week or so, so he couldn't finish. Bad luck, the neighboring school's Piper, which he MIGHT have been able to use, was getting a paint job...
I'd advice you to go for the C152 and get your instructor to book your lessons as early in advance as possible. I haven't taken that step yet, but everyone says converting after finishing the PPL is pretty straightforward, so I'd pick the aircraft which gives you the best experience DURING the training and don't worry about what happens after that...