We were just on Ambergris. We didn't dive with Protech, but we did get some nitrox from them (they are currently the only ones on the caye with nitrox - soon to change). They do have the only shop there that you can purchase gear, replacement parts, etc, but being the only ones, they're a little pricey. We dove with Aquadives (part of the package) and had a pretty good experience. Our only complaint was the groups were a little too crowded. Protech claims to assign no more than 6 divers per DM.
As for accomodations, it depends on what you want. There are a lot of nice places to stay on the caye. We stayed at AquaMarina Suites and really enjoyed it. The selling factor there was the kitchen in the 1 bedroom suites. We shopped at the local groceries and ate breakfast and lunch in the suite every day. A lot more convenient than trying to find somewhere to eat right before and right after diving. By the time we finished our 2nd dive each day it was around 1230-1pm. Throw a shower in there and lunch would have been at 2 or 3 otherwise. We then ate dinner out.
No matter where you stay though, the dive ops will usually pick you up right on the dock outside your resort every morning and drop you off there every afternoon. Hank pretty much hit in on the head with the description of the diving. Do request Victoria Canyons and Eagle Ray Alley. That's where we saw the most marine life - nurse sharks, spotted eagle rays, and sea turtles.
