An option is to take a taxi to the muni airport (about $15) and Tropic Air from there. They leave every hour and it is half the price of flying out of the International -- and less time.
Personally, I like going by water. I want to get as close to the water as soon as I can. I like the camaraderie and excitement of the boat. Lots of local people. I start taking pictures right there. I want to feel that I am IN BELIZE from the time I land.