I have not done Coz, but have many friends that have done it a lot. I'm going to Coz on their recommendation in Feb. 2006. I have done Bonaire, though. The food was just OK everywhere we ate, and the service was very slow, but we didn't really care. Not much in the way of night life, so if you want to party, not the place to go. Of friends that have dove both places, most prefer the diving in Cozumel. Shore diving is nice in Bonaire and you can get much more diving in for the price but it's much more work, especially if you have some windy conditions. We got pretty beat up several times trying to do beach entries. As far as bottom time goes, all the places in Bonaire only use 80 aluminum tanks. If you get the right dive op in Coz, you'll be using steel 120's for plenty of bottom time. We plan on using Living Underwater. Aldora dive op also is known for fast boats and larger tanks, but Living Underwater is a bit cheaper, provides a few more comforts, and are a little more flexible. They'll pretty much pick you up whenever you want and they don't charge more for twilight and night dives. Also, reviews show that they're good at tayloring dive sites to what you want to do, so if you want a nice slow dive, out of strong currents, they'll give it to you.
Which ever site you choose, I'm sure you'll have fun. Getting to Bonaire is another story. I'm willing to bet it would be easier to get to Coz.....and cheaper.
Have fun!
