We went to Lamanai with Tanisha Tours. Long day, left the dock at 7am, didn't return until 6pm. For us, the trip was half the fun. We saw lots of wildlife, including dolphins on the ride back. The ruins themselves were awesome. I can't think of any good reason to need time on your own, without a guide, they really aren't nearly as interesting. All in all, a trip I"d definitely recommend.