I like both islands but for different reasons. A long weekend will last longer on Caye Caulker. The pace is slower and less crowded than San Pedro. BUT the food opportunities are just as good and there are a couple of great places to hang out. We stayed at Seaside Cabanas in February for 3 nights and had a great time. Then headed over to San Pedro for a week. Perfect vacation for us. In fact doing it again in February 07. Friday nights at the Oceanside are pretty fun, good music and good drinks. And if you go to Caulker, have breakfast at Amor Y Cafe. It is really good.
If you decide on San Pedro, take the water taxi to Caulker and check it out.
Whatever you decide, I know you will have a great time!!! cool cool cool