The one thing I really don't like when flying the 172 is that my head is essentially *in* the wing (I'm 1.86m). This very much limits the horizontal view out - which is where the traffic is that I'm worried about.
Other than that, horses for courses really. Both are very docile planes with about equal performance. And both within the PA28 and C172 fleet you'll find clapped out planes with torn seats, stone-age avionics and that typical 30-years-of-vomit smell inside, and brand new, leather seats, state-of-the-art avionics and new-car-smell ones.
It's easy enough to stay current on both, so why not try them both and only decide what you're going to fly on the day itself, depending on availability and mission?