Ramon's, Xanadu & Exotic Caye would be the ones on your list that are the most different from what you would find in the US. Very tropical looking. BYC and Bz Shores are fairly hotel-ish looking. And if you are intersted in drinking and dancing nightlife, North is not where you want to be.

Xunantunich is a long day trip from SP. Stick with Lamanai or Altun ha for ruins. No need to spend the night in BZ City unless you want to.