I’ve been to Bonaire but not to Curaçao so I always like to hear the comparisons of the two.
Been to Bonaire 9 times and Curacao one dive trip (all boat dives). In researching the issue, here are differentiators from what I've read or been told:
1.) Curacao is a good deal larger than Bonaire. Looks about half again as large, just eye-balling it on Google Maps.
2.) The capital, Willemstad, is much more developed looking than Kralendijk, with taller buildings with more stories (but still that pretty Caribbean color and architecture), things you just don't find on Bonaire (e.g.: Queen Emma pontoon bridge that swings, plus a suspension bridge elsewhere).
3.) The Willemstad area has more civilized entertainments - such as the Curacao Sea Aquarium (neat place; you can do paid dolphin encounters).
4.) Stronger reputation for more sandy beaches.
3.) and 4.) make Curacao a better bed for non-divers.
5.) I liked the diving to the east, but it's often said it's better in the Westpunt area. That said, I'm told Westpunt is about 45-minutes from Willemstad and quite rustic.
You know how in Bonaire, if you stayed at Caribbean Club Bonaire Resort out near Oil Slick Leap, you'd feel isolated but Kralendijk would still be a pretty modest drive 'to town?' Well, if you're in Westpunt, that's a much longer drive.
6.) Bonaire has a coast-hugging road that takes you right by dive sites. Curacao has an analogous road further inland, and you take take turnoff roads to reach shore dive sites. It's longer between sites, but some people do a couple of dives at a site so they don't try to rack up as high a 'site count' as Bonaire divers do.
7.) Curacao shore sites are described as often having easier sandy entries but longer swim outs.
8.) Some Curacao shore sites are like Bonaire (rustic, just you there), and some have 'facilities' (e.g.: a restaurant, dive shop, showers, etc...). There may be a fee. Some people at some shore sites rent tanks from an onsite provider rather than just haul tanks around from their 'base' dive op.
9.) People heading out of their home base in a rental pickup with a pile of tanks in the back doesn't seem quite as dominant an image in Curacao, from what I've read. Not sure why not, but judging from trip reports, more people do at least some boat dives rather than the all shore diving many Bonaire divers do.
10.) Sometimes Curacao airfare may be a bit cheaper.
Curacao Trip Research Notes
Curacao Trip Report with SB Surge Jan. 2019
On the face of it, Curacao seems to have a lot more to offer, but the full extent of it is more spread out. I keep ambivalently considering a solo trip to Westpunt to try All West Apartments or Nos Krusero and use Go West for diving...and then shifting into Bonaire trip planning because I already know the place fairly well and it's just so easy. The one shore site amenity I wanted was answered when some food trucks started operating in Bonaire.
But heads up for the future. I keep reading of how crowded some popular shore dive sites in Bonaire have been lately. If that keeps up, and given that Bonaire's government seems to have the attitude they've maxed out on socioeconomic benefit from divers and that's not enough so it's time to cater to other forms of tourism (and things are getting built up), Westpunt may be starting to look real good in the not to distance future.
Hope I got all that right. The Bonaire vs. Curacao debate has been a key interest on ScubaBoard for years.