AB&C are all fairly different experiences. While the islands look close together on the map and seem like they should be fairly similar, they're not. They are each located differently relative to the continental shelf, so things are different underwater. Things are pretty different above water too. I went to Aruba once long ago before I dove, it's a nice place for a beach vaca, but most people don't really seem to consider it a dive destination compared to the other 2. It is much more about (heavily North American) mass market tourism than Bonaire or Curacao. Bonaire is very heavy on dive tourism, there are some other things but it really feels like a divers island. Curacao is larger, more populous, and has more of a varied economy - while there's plenty of good diving and some dive oriented places to stay, it's a much smaller part of what's going on. (That has it's pros and cons.)
Bonaire is a great place to take a new diver, and do lots of shore diving, and not have to worry much about currents at any of the commonly dove sites. That pretty much applies to Curacao as well. On Curacao It's not quite as convenient to drive from one shore site to another as Bonaire because of the topography of the island and the way the roads are laid out. OTOH, the sites have more variety, and tend to have easier entries from beaches rather than ironshore. I'd say on Curacao there's more chance of a current in some places, but I wouldn't expect anything that is a big deal.