That's a tough call. In summer the CA will most likely make it over to the Sisters so you've got the Tibbetts and Bloody Bay Wall. I've dove Grand Cayman from shore and many of the GC sites they do are also short boat dives. Every trip report ends with their dive at Devils Grotto. I swam 100' to it from Eden Rock's steps. I have a hard time paying for dives I can do from shore so I've personally never been that big a fan of CA, I'd prefer to spend a week at LCBR instead. Obviously you get all three islands for the price with CA. Given how expensive everything is on Grand Cayman, a week on Aggressor is probably a lot better deal.
We did the T/C Explorer a few years ago. The best diving was at West Caicos and French Cay. In fact I could've skipped NW Point entirely - except the boat boards there since the airport is on Provo.
Plan to see sharks on every dive at French Cay. Every single dive we saw a couple. Turtles, barracuda, lots of macro life. I spent probably most of 2-3 dives filming the macro life around individual coral heads 100' from the mooring. Fascinating when everyone else leaves and the small fish come out. One night we watched the sharks feed 120' away in the bow lights. Probably saw 100+ Stingrays over several days. Only local boats from Provo go out there besides the two LOB's so nothing is bothered by divers. Some of the walls are pretty spectacular, over one a DM told me the next big plateau was at 1000' on it's way to 6000'.
Mike Southard wrote a good trip report - probably a couple years before us.
Saudio's Trip Reports
We looked at both boats, I chose Explorer:
They offered $400 off a week we could go.
All the cabins except the lowest priced three are main deck or above. And all have beds and big windows except the three below deck. Our room had a large nightstand between the beds and a corner desk. So plenty of places for cameras etc. Even a decent sized bathroom shower - I'm 6'4" so the door was a little low but otherwise it was fine. Stan the cook is legendary.
Explorer also has a flybridge one deck up from their main sun-deck. Tables, benches, covered, they stock drinks. Nice area, I even slept up there a couple mornings.
They vent the compressor heat thru the center of the dive deck and the suit hanging rack is above it. So t-shirts/shorties dry between dive sets. I dove all week in dry clothes, t-shirt and microfiber board shorts. Stan the cook is legendary.
Explorer swings on it's mooring - a lot. So if it goes by, you just wait 5mins. for it to come around again. Once I tried to catch it from about 15' away but literally couldn't. Rougher seas and some current that day, we'd been drifting nearby earlier.
The Aggressor is all bunks, all below-deck, all portholes. I think slightly more expensive also. At least 3x they were at the next mooring over. Once I swam up to and under it not realizing it wasn't ours. So I popped up and took a close-up look at it from the waterline. Nice looking boat. They bundle Nitrox, Explorer charges extra. Since I don't, I saved $200.