I did about 50 hours in a 152 before heading back to the UK and am now flying a PA-28... I loved the 152 for it's old charm (It was actually 2 years older than I am!) But when I first got into the PA-28 I could feel the difference in quality.
Granted it's a newer plane with 2 extra seats and has a slightly more powerful engine, but everything just seems to be more robust and in a sensible place (To me)... Also you get a proper throttle and not a plunger!
The only thing I would bring over from the 152 to the PA-28 would be the electric flap selector, that's a nice touch compared to the handbrake style one in the 28.
In answer to your question I wouldn't worry too much about your choice of plane as both are similar, however as 172driver and Paris Dakar have said, once you have chosen, stick to it for your entire training to get some consistency in. Convert once you have the skills necessary and I'm sure it will be a fairly smooth transition.
One question though, why on Earth did they only include one door in the PA-28?! I'm sure there's a sensible answer, but I can imagine a few questions coming my way when I finally take up some friends... I'll look it up!
Good luck with the flying!