I just came back from Grenada on Monday after doing three days diving with Aquanauts and staying in True Blue, and a week on Peter Hughes Wind Dancer.
True Blue is a really nice resort, with good food, a decent bar, spacious, comfy rooms and, best of all, it is right next to Aquanauts.
Can't say enough good about Aquanauts. One of the most-professional, well-run dive centres in the Caribbean. Three boats, all a decent size and capable of taking 16-20 people (though they never cram that many on), excellent knowledge of the wrecks and reefs, and enough sense to treat experienced divers as experienced divers and let you dive your computer profiles.
Their specialty is the Atlantic wrecks, such as the King Mitch and the Hema 1, and they are awesome. Blue water, 35m plus depth, well over 40m vis, lots of marine life (cuda, nurse sharks, eagle rays, stingrays, etc). They also do great tours of the Bianca C, though she has degraded some since I was there four years ago.
Contrary to popular belief, I think the Grenada reefs are fair healthier in terms of fish population and coral/sponge growth than anything in the northern Caribbean. Tobago, Grenada and, to some extent, Dominica can also serve up sites with enough fish to make you think you were in the Indo-Pacific. On one dive last week, my buddy and I got into the middle of a massive shoal of 2,500-plus southern sennet and it reminded me of Ras Mohammed on breeding season!
Big thumbs up from me!
Mark