I've dove only Bonaire of those. To me, of the ABC Islands, first decide what kind of diving you'd most like to do; shore diving or boat diving.
It's my understanding from others that Aruba has some good wreck diving. But it'd mostly be boat diving in Aruba. I've done boat dives in Puerto Rico, St. Thomas and Grand Cayman (2 tanks each). In a nutshell, my experience with boat diving is basically that for about $125 per head, you get taken out about a half hour or so, listen to a dive briefing including discussion of getting out of & back on the boat, a group you're a part of jumps in the water one after the other, and when everyone's in they sink and the Dive Master leads the group on an underwater sight seeing tour pointing out known points of interest like green morays, etc... Actually a lot of fun. I'm not saying all boat diving has to be like this; some will let experienced divers do their own thing, for example. And this may be just what you want.
With Aruba you get casinos & other activities that may appeal to non-diving family members. Beautiful sandy beaches, too.
Bonaire is famous for shore diving.
Here's a link to my trip report, with photos & discussion as a brief intro. to it. In a nutshell, you probably stay at a hotel near the beach on the west coast (which is the calm side that people dive on). You've likely got a package plan were you get unlimited scuba tank usage; they put out pre-filled aluminum 80 cf tank, you load a couple/diver in the back of your rental truck, drive around to any one of many shore sites marked with yellow rocks, park, gear up, and walk in. Entry can be tricky at some sights due to rough rock with waves washing over it; plan to put your fins on (& take them off) when you're out in waist deep water. You swim out maybe, oh, I dunno (lousy judge of subjective distance), maybe 50 to 100' or so, and that's were the sandy bottom drops off at a roughly 45 degree angle, becomes the reef, and you dive over that. When you're done, surface & swim ashore. Basically, if you want to dive 3 or 4 times per day and squeeze in a night dive, that's fine (although being Nitrox certified helps for those who want to do repetitive dives). Do it appeals to hardcore independents who want to dive a lot & don't want to put up with boat rides & rigmarole or play 'follow the leader' to a Dive Master. But the visibility is so good, the water so warm and diving near shore with (in many popular sites) little if any current so nice that it's good for newcomers, too (assuming they watch their depth gauges; it's easy to dive much deeper than you think you are, because 80 - 100 feet looks & feels about like 30 - 40).
Bonaire has little in the way of sandy beaches. My experiences are with Eden Beach Resort & WannaDive dive shop. This resort as the main sandy beach, from what I've heard, and it's nothing like what you'd see in Aruba. So, if you've got a spouse or other tag-alongs for whom roasting like a lobster on a big, scenic sandy beach is a big deal, might be a deal breaker.
Bonaire is larger than Aruba but much less densely populated. You can enjoy some scenic coastal views at the north end (Washington-Slagbaii Park), watch kite surfers further south, enjoy the tropical arid countryside (lots of cacti) and flamingos & visit the Donkey Sanctuary. A non-diver MIGHT get bored on Bonaire; depends on the person.
Curacao vs. Bonaire is discussed in some threads in the ABC islands subsection of the forum. From what I've read, Curacao is larger, the economy not as focused on diving, the shore diving is available but maybe not always quite so 'multi-site in-your-face' in terms of cookie cutter package deals (if I understood right; may be way off on that), has several good sites to shore dive (not as many official sites as Bonaire), and may have more to offer non-divers (so some say; I haven't been to Curacao).
From what I've read about Saba, it's very 'rustic,' so if you like the creature comforts of a large resort or civilized entertainments like a casino, might not be your thing. If you like a REAL 'getaway' and pinnacle diving to submerged peaks, might be nice. Some people on this forum love Saba, from what I understanding. Sounds like a rather unique diving experience.
Richard.