Pumps are great. But, for even better versatility, an U/O is probably your best bet. Before I get flamed to burnt toast, I should add that my personal preferences run to classic side-by-sides, certain pumps, and cool stuff like lever shotguns and revolving chamber shotguns. My tastes are irrelevent, however, because I have the luxury of buying each gun for a particular purpose - which brings me back to versatility. For everything from trap, skeet, sporting clays, down to upland birds, migratory, and small game, U/O's can do it all. 20 gauge is best for many of those, but once again, 12 covers them all at least adequately.
SUMMARY: Go with U/O in 12 gauge (if versatility, durability, and reasonable cost are your primary drivers).