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Turtles, eagle rays, king mackerel, schools of jacks, snapper, and permit are all common in Belize and rare or non-existent in Bonaire, in my experience.
I've done Bonaire and Belize each twice. You will definitely see bigger stuff in Belize. If I was going back to either I'd pick Belize, unless I was set on doing 20+ shore dives in a week at Bonire for the same money as 12 or so boat dives at Belize.