I've been to both (Bonaire 05', Curacao 07'). In some areas the diving is very similar - same fish, corals, fans etc. At a couple of Curacao sites I told my friends: "this is just what it would be like on Bonaire" We probably saw more critters on Curacao, seahorses, several different kinds of lobster/crabs, a couple octo's and more squid than on Bonaire. Probably saw more turtles on Bonaire. Never saw a shark at either location. We stayed out in Lagun (Curacao) a couple of days - twice in the morning a pod of dolphins cruised right by our place.
Other areas are different - there's nothing similar to the Mushroom Forest area on Bonaire. Or the Carpile wrecks. Overall there was more trash in the water in Curacao.
Although everybody says Bonaire is all about shorediving, I know several people who only boat dive there. Trips are made to the 20+ Klein Bonaire dive sites and the more difficult to access shore sites - like Rappel. Small Wall and 2 other sites are only accessible legally via boat as they're off private property. I've even heard of people doing boat dives on the Hooker, that might be a better option as a DM told me he likes to dive the 2nd reef past the Hooker and then drift back onto the wreck.
We did 4 mornings of 2-tank boat dives and shore dove every afternoon. It was just about right IMO - a good mix of dive sites. A lot of the Bonaire shore sites start to blur later in the week, they're very similar in appearance/fish life as they're on the same reef.
At several of the resorts, I would've had no problem finding a buddy, I was asked two or three times while waiting for my buddy at Habitat and Bonaire Dive/Adventure. On the final leg of our AA Bonaire flight, I think just about everybody was a diver.
On Curacao you'd also have options as a single diver. Ocean Encounters is probably the largest operation on Curacao, they have a main location at Lions Dive/Sea Aquarium and 3-4 satellite facilities at Breezes, the Hilton and a couple other resorts nearby. Our only boat dive with them was the Dolphin Dive, only about 8 of us that morning.
They also have a facility in Westpunt (OEWest). So you can access most of the better mid-island dives from town and the Mushroom Forest and Watamula from OEWest. It's about a 45min. drive out to Westpunt from Willemsted. Longer than it looks on the map. Neither OE or OEWest allow solo diving.
Watamula is supposedly the best boat dive off Curacao. Playa Kalki/Alice in Wonderland is IMO the best shoredive - it's off OEWest's dock. We only did one boat dive on Curacao - Lost Anchor - it's not a site that's easily shore accessible as it's fronted by a cliff. It was a good drift dive, look for seahorses if you go there.
Another option you'd have is to shoredive with the
Dive Bus - they pick you up and dive all over the island. There's nothing like that on Bonaire.
I'm not a photographer - I shoot video. If I had to pick one location over the other for macro, I might give the edge to Bonaire. Salt Pier is a photographers dream, amazing lighting and growth on many of the pier structures.
