This has been done to death numerous times before but as someone who does roughly similar hours in each (both 160 HP) here's a few thoughts (with a bit of UK:US perspective thrown in):
Performance: nothing in it except the 172 feels slightly more relaxed on short fields, maybe 'cause the wing is further from the bushes.
Convenience: C172 far better with two doors, but PA-28 far better for luggage space and access. C172 ('R' and up) a right pain to check tanks (13? drain points!). All C172's a pain to fill up (not in US, where someone always rushes to do it for you!). And less you remember the fuel selector, many C172's will drain your fuel away overnight if there's the slightest tilt.
Sightseeing: C172 far better in most situations, excepting over the water, when the PA-28 wing between you and the sea offers a degree of fools' comfort. Opening windows in C172 a huge bonus for photography.
Efficiency: C172 mixture control allows much better leaning control that the Briggs n' Stratton lever fitted on the PA-28.
Safety: Nothin in it, except the C172 is far more likely to blow over (or away) in strong winds than the PA-28. Not a factor in the US where there are always tie-downs.
Availability: as said already, in UK typically PA-28 much more available than C172. In US, very much the reverse.
Style: Taking someone flying in a C172 sometimes leads to a "is that it?" moment. On the other hand, the PA-28 once generated an "Oooh, it's just like a real aeroplane" from a young relative. So if young ladies are on your itinerary then that's a vote for the PA-28.
Preference: Do fly them both. In UK, PA-28 has a slight edge because of availability and possible escape from a ditching. In US C172 is a clear winner on grounds of sightseeing and again, availability.
All views expressed are personal and probably rubbish!