Squawkident, as my handle says, I do fly 172s quite often, albeit usually the RG version. I did, however, learn to fly on PA-28s (both the 160 and the 180 hp variant), so feel I know both. And no, I am not obsessed about this.
To start: fuel consumption will probably be very similar, depending entirely on the individual machine. Don't worry about that aspect.
The main differences in no particular order are:
Doors: Cessna 2 / Piper 1. You can enter and exit a Cessna 'normally' without climbing up a wing and then into your seat. You hint at size being a factor in moving up from a 150, in which case a 172 will definitely give you more comfort. All in, a 172 is a much roomier a/c than a PA 28.
Views: you see more from a Cessna, important perhaps more for the pax than for you.
Flying: the Cessnas have a much lower wing loading, some people feel that makes them a bit 'nervous'. I'd agree that a Piper usually feels more solid in the air. However, the service ceiling of a Cessna is considerably higher than a Piper. As for short field, a quick glance at two of my POHs shows the Cessnas are somewhat better in this regard.
All that said, availability is always a concern and you say that your club has a few PA28s and one 172, so think about this also. Of course, this can also mean, that most people fly the PA28s and you'd be the lone 172 guy
