As others have said, very little to choose - I've flown PA28's (from -140 up to Archer) and C172's (including the new, fuel-injected SP).
The only bit of real feedback I would give, based on personal experience, is that you may learn how to land better in a 172:
- full flap landings require accurate control of speed and power settings
- more reactive to x-wind, due to high-wing config
- "greasers" easier to achieve in PA28 due to "ground-effect" (but too fast on a warm day and you will "float" forever)
- take-off's a different ball-game though. 172's seem to reach the correct speed and fly-off, whereas PA28's (especially the heavier Archer) need quite a marked haul back to rotate.