With 5 days I don't think you want to spend parts of two of them transferring to LC or Brac? Resorts are limited, restaurants also. My sister owns on Brac at one of the better known condo resorts - their beach is marginal.
SMB is a very nice beach. It's a little nicer/wider on the north side plus along the south end there can be iron shore at the water's edge. here's an example of that, this area is south SMB fairly close to Georgetown. See the little circular breakwater off to the right in one shot - I've stayed there - the beach was as bad. From the Westin north it gets nicer.
Grandview Condos in Grand Cayman
There can be 4-5 cruise shIps in port some days so it's best to visit Georgetown after they leave - typically around 4pm. Some good restaurants and they'll be less crowded. You will actually see the ships moored in the harbor from many locations on SMB but about the only noticeable impact (Besides downtown) is the tour buses going by occasionally or the 500 or so cruisers playing with the Stingrays at Sandbar which is near but not Stingray City which many dive boats dive in the afternoon.
None of the "dive" resorts have much/any beach so I'd find a SMB property you like and let the dive ops pick you up - most will anywhere along SMB. Also when you're not diving, there's other things to do just behind SMB (Caymana is one) as well as other watersports on the Sound. Many of the dive boats shuttle you to marinas nearby in that area also and dive either North or West.
If you don't have preference - or budget limitations - the Westin is pretty nice. Red Sail Watersports is onsite there but they cater to some cruise traffic (Disney) so might have larger boats/more divers.
Don Fosters downtown has most of the cruise contracts.
There's quite a few 6-8 divers max - many with boats big enough for twice that. Cayman dives all run around 2/$100 so often service is what drives repeat business. Here's most of them -
www.cita.ky.
Turtle Reef is arguably the best shore dive. It's at the Cracked Conch restaurant property -
Sun Divers — Cracked Conch Macabuca Sundivers is onsite for tanks etc. Easy entry, shallow mini-wall just offshore. If you follow it left you'll find the Tarpon Cave plus you should see Turtles - they get out/are released from the Turtle Farm across the steet.
Also have some dive sites in mind as you;re often asked.
www.idivecayman.com lists most of them with videos. Orange Canyon, Big Tunnels, Ghost Mountain are good dives. If the operator you pick won't go to GM call DiveTech and see if they are - they're at Lighthouse Point north of SMB so you'd have to drive there but it's also one of the better shore dives