I have to agree with some of the comments here about the PA28's handling abilities. When I went from C152-PA28 I was majorly disappointed (Especially cos I'd bought the share!) It felt like a flying tank compared to the C152. However, now I'm used to it, it's a great aircraft.
Getting in and out of the PA28 is no where as easy as the C172. The whole "one door out to the wing" bit can be annoying. You can quite happily slip in and out of a C172 from both sides, no problems. (Same can't be said for the C152!)
IMHO the PA28 is much more comfortable in the cruise, less noisy and has better performance. Also, I find the C172 quite nose heavy.
Having said that, I'd still be happy to own a C172 share.