If I were doing a dive only trip then my choice would be Bonaire. It's a lot smaller and more laid back than Curacao. I would consider Curacao if I have non-divers going with me. Bonaire is pretty much dedicated to eat, sleep and dive, which is what I want in a dive vacation. Curacao has more topside things to do without getting to touristy. The dive sites are similar but IMO are easier to get to on Bonaire, mainly due to the size of the island. With the exception of the park, almost no dive site on Bonaire is more then 15-20 minutes away from any resort, on Curacao almost all the sites are over 20 minutes if you are staying near town (or town and most restaurants are 30 minutes away if you are staying at some of the resorts near the dive sites). Almost all the sites on Bonaire are undeveloped, somewhat isolated and you are on your own. Many of the sites on Curacao are pay to dive sites. The cost is only a couple of dollars per day and the facilites are pretty nice so the cost is well worth it. Curacao is also a little easier to get to, Bonaire can be a pain. You can't go wrong with either island.