I'm pretty sure Ft. Young uses the dive op from Castle Comfort for their diving operation. I didn't stay at either but stayed at the Evergreen right next to Castle Comfort. Big difference between Ft. Young and Castle Comfort. Ft. Young is definitely the nicer, it's also right in town which makes it more convenient for walking to different restaurants for dinner. People seem to like Castle Comfort but is definitely a "divers hotel", nothing fancy and a little run down around the edges. Ft. Young is more modern. At Ft. Young both the regular restuarant (expensive) and the bar resaturant (reasonable) were very good. The food at Catle Comfort was okay but not great. Though we did like the outside palapa bar for drinks before dinner.
When we stayed at the Evergreen a couple years ago there was a niteclub operation a few blocks away (Cocunuts I believe). Two times during the week they played booming music till 5 AM in the morning. It was hard to sleep. If they are still there there is no way I'd stay at Castle Comfort or Evergreen. If we head back to Dominica we'd probably stay at Ft. Young. But we'd also probably make the 20 minute drive each day down to Nature Island Dive and use them as the dive op. Much smaller groups than with Dive Dominica. Most people seem to like Dive Dominica, it's just a preference thing with me, I'll take small group diving over larger groups any day. When we were there we did one day (2 dives) with Dive Dominica (13 divers) and 5 days (11 dives) with Nature Island Dive (averaging 3 divers per dive), with 2 of the days it being just my wife and I, sort of like private diving with a DM.