Everything herman said^.
One other advantage Bonaire has is that just about everybody buys the shore dive pkg. including a small 4-door truck. So it's fairly easy for a couple of divers to accommodate a third for local shore diving. And most everybody there is a diver or related to one. Almost all the bars, restaurants, the Houston red-eye on Fri night/Sat morning, will be full of divers. We had two potential dive buddies by the time our flight took off - my buddy's t-shirt encouraged people to ask.
Also while waiting for my buddy at both Bonaire Dive/Adventure and Habitat - I was asked if I needed a buddy. We dove with Toucan Divers at the Plaza that week - anytime there was a single diver on the boat they were encouraged to stay near the group or pair up with the DM - probably the best idea since they find all the good stuff.
All the ways to get there:
Info Bonaire - Airline Information and Connections
One advantage Curacao has is that there are shops at almost all the shore dive sites. But that doesn't necessarily promote finding a buddy. The only place we were asked there was at Porto Mari - a locals beach in addition to being a great dive site. I expect Lions Dive might be another good place but I've not stayed there. The difference being that on Curacao most resorts offer diving - on Bonaire many of the waterfront resorts
are dive resorts. At several of the shore dive sites we were the only ones diving for several hours.
---------- Post added December 29th, 2013 at 06:24 AM ----------
My other suggestion might be one of the AI resorts on either Roatan or Grand Cayman. Since they're more isolated, they're almost all divers generally. Cayman's pretty expensive though. One advantage to Roatan is you won't need a car. Several of them offer airport transfers as part of the price.
Look at Cocoview, Reef House Resort, Fantasy Island Beach Resort or Anthony's Key on Roatan. Barefoot Cay is a little more upscale and smaller - they also get non-divers there so might be harder to find a buddy. Sunset House or Cobalt Coast on GC. All also have shore dive options right off their property. If you're looking for something to do at night, AKR is 5 mins. by cab ($6) from Roatan's West End which is where all the nightlife is. Similarly Sunset House is walking distance to downtown Georgetown.