Using a PA28 would really have no practical benefit in the training environment. The Warrior is more comfortable than a 152, but that's about all.
If you're going to stop at PPL, the Warrior is a more useful aeroplane, but training-wise, if you move from the 152 straight into a CSU (e.g. Arrow/Dakota/182 etc) it would be no harder than moving from a Warrior into the same aircraft.
The extra speed (all of about 10kts) of a Warrior is basically irrelevant for training because you're flying the same number of hours regardless of which aircraft you fly. The only difference would be you could go a bit further on your navs in a Warrior.
I'd stick with the ol' 152 and save your dollars. Maybe even consider using that saved money towards doing your CPL on a multi.