Glad to see you're about to go for "the real deal". I'm assuming (hoping) that because you're 3 years past your cert, but with no dives at all, not to mention in the last six months, that you'll do a refresher of some kind before you go, or FIRST thing on your arrival at your destination. At this point, I'd say your newly certified friend is more prepared to dive than you.
If I were to assess just the diving, I'd say go for Bonaire over Ambergris key (IMHO). But as a first-time trip, I'd recommend Ambergris Key. You'll have a greater concentration of dive operators in a smaller area, and explaining your experience to the dive company, you'll be sure someone will be checking on your performance. Of course, you still need to be sure you're diving with a company that has a record of responsibility. Go read other threads in the Belize forum, and you'll learn all you need.
Now you can do all of that in Bonaire, but it's very largely geared toward shore diving (almost always free of a divemaster). It's a great experience, but one for someone who is pretty confident about their gear and diving routine. Maybe later ...
If you're on a budget, I'd recommend Patojo's for a dive company on Ambergris. Small groups, their DM's (especially Tony) are helpful and a lot of fun (Chabo is downright nuts!) but safe, and you can bargain if you say you'll do "X" number of dives with them, so what's their best deal. If they don't suit you, you're about 50 feet from plenty of other operators.