There's not a whole lot different in my opinion, I'm currently flying both. The C172 has better visibility, especially for passengers in the back, but I kind of prefer the Piper over longer distance, the 1 door thing is crap though especially when bringing passengers. My personal view is that Cessna=4X4, Piper=(1 door)Saloon
I wouldn't worry about what you're flying afterwards either, I jumped straight across from Piper to Cessna, it was seamless. Maybe as previously stated the C152 is the best way to go, cheap and harder to handle if previous commenters are correct.