I just came back from Caye Caulker yesterday. There are definitely some newer developments (both hotels and rentals) that, whilst not luxury resorts, are very well finished and probably exceed a mid-range European or US hotel. We stayed at Weezie's Oceanfront hotel and cannot recommend it highly enough - right at the sea, beautifully designed modern rooms overlooking the ocean, pool, spotlessly clean. They also have three inland cottages.

Do note that both Ambergris and Caulker have no proper beaches - the coastline is made up of mangroves and sea grass, but many places have piers which it is possible to swim from. I hear Placencia is much better, if long sandy beaches are a must.

Snorkelling: had a couple of extremely well done tours which actually turned into private trips due to it being low season, from Caveman tours and Mario's tours for a full day and night snorkelling respectively - both highly recommended. Pretty sure that those guys take fishing tours as well, though I didn't take one.

I was briefly on Ambergris during a diving surface interval. Much bigger and more commercialised than Caulker - it reminded me of Roatan with much more happening, but also less characterful. Nothing wrong with that - just not my preference.