Curacao over Bonaire for me also. Diving was more diverse - a lot of South Bonaire looks the same after a few days. Diving facilities are superior on Curacao also. Downside is they're more spread out. On Bonaire your resort has a shop and house dive. Some on known dive sites. Once you leave town there are no facilities at any dive site either north or south - none. Most entries are over sharp coral rubble and ironshore at the water line and into the surf line. So they're tricky.
On Curacao the reef starts a short swim out at many of them. So you enter off a sandy beach or the few that have ironshore also have a dive dock. With 3-4 exceptions every dive site on Curacao also has a very nice beach with full facilities - on site dive operator, some sort of restaurant/snack shop on site. And the all important shade. (and bathrooms) All of them are known dive sites also. Many of the hotels also have on-site dive shops and house reefs. I will give the nod to the better house reefs being generally on Bonaire. Except Playa Kalki listed below - the house reef for Lodge Kura Hulanda (and All-West Apts.)
The best dive I did on either island was Playa Kalki in Westpunt Curacao. The 2nd was Vista Blue on Bonaire. Subjectively the next 1/2 dozen were almost all on Curacao. I do like Salt Pier on Bonaire but the Tugboat site on Curacao has both a pier and the Tugboat. I'm not a wreck fan but I understand that Superior Producer (basically in downtown Willemstad) is a better wreck than the Hooker in south Bonaire.
As a overall vacation spot also. Bonaire is diving, a few decent restaurants (a couple excellent), kitesurfing at Lac Bay and the Donkey Farm. Slagbaai Park but bring a spare tire. Nightlife is Karel's Bar, Havana Cafe, the Divi's small casino or the bar at your resort.
Curacao has nightlife, dance clubs, multiple casinos, many more restaurants, (some excellent), the Sea Aquarium, famous shopping downtown, Ostrich Farm, Christoffel Park, Hato Caves, Substation Curacao (deep sub) etc. You can dolphin dive also at Ocean Encounters near the Sea Aquarium.
Curacao for most people is easier to get to also. Unless you can do the direct red-eye to Bonaire from Houston on Friday night. Or Delta from Atlanta. I dive with a group of friends in different locations in the U.S. We were all able to get to Curacao by about 2PM. We couldn't get to Bonaire before dark unless we took the red-eye - starting out early morning. But I live in Phoenix.
Never been to Aruba or St. Maarten.