Reading some of the Curacao vs. Bonaire threads is an enjoyable way to kill some time. I've been to Bonaire 8 times; haven't dove Curacao. Drawing on what other people have posted, if I understand correctly, the differences are something like this:
1.) Curacao is bigger and has a larger population and 'more topside stuff' outside of diving.
2.) Both have similar diving.
3.) Bonaire has a long road running down the west coast (where people dive) that often nearly hugs the shore line, and lots of named dive sites are close together down the west coast. So, you can find sites easily and get in a lot of diving (say, 4 or 5 dives per day), which can lead an avid diver to average more dives in Bonaire.
4.) Curacao has a road that's farther inland from the coast, and you often take side-roads out to dive sites, which means more driving between sites.
5.) Curacao has a number of easier sandy entries, but at the cost of longer swim outs.
6.) Some Curacao shore dive sites have onsite businesses that may offer amenities for a fee. Just what and what prices you'd need to research the threads for.
7.) Someone once posted to the effect that the 4 door pickup with tanks & gear in the back driving up & down the coast of Bonaire isn't quite what you see as much of in diving Curacao (mainly the truck was mentioned), but I don't know what the 'diving workflow' looks like in mainstream Curacao diving so perhaps someone else can share about that.
8.) While Curacao has no blanket prohibition on solo diving, some of the main dive operators there do prohibit it. On the other hand, I know of 2 main Bonaire operators (Buddy Dive and Dive Friends) who allow it if you're solo certified, and 2 more (WannaDive and the technical dive op. located at Captain Don's) that teach the SDI Solo diving course, so I'm guessing they'd allow it, too.
9.) From the U.S., airfare to Curacao is often considerably cheaper than to Bonaire.
Bonaire has boat diving but is heavily sought for shore diving. Curacao also has both. I usually hear of Aruba being mainly a boat diving destination.
Apologies in advance if I've made any mistakes, and I imagine any will be corrected promptly by others. I'd tried to summarize here, but the threads discussing it with 1st hand reports are worth a read.
Richard.