None of the above.
If you're somewhat flexible with travel plans, one option is get to Puerto Penasco, Mexico by THIS SATURDAY - July 20th - the liveaboard Rocio Del Mar has 2 spaces left. $2295 for the week.
http://www.rociodelmarliveaboard.com/midriff.html
They're diving the Sea of Cortez - Midriff Islands this summer -
Legendary diver Jacques Cousteau described the Sea of Cortez as the "world's aquarium" and the "Galapagos of North America.” Dive on untouched walls and reefs abounding in marine life. Encounter great and small whale species, whale sharks, manta and jumping mobula rays, and sea lion colonies.
Good diving, my buddy did it last summer.
Fly to Phoenix, AZ - it's a USAirways hub and they codeshare with British Airways. Virgin also flies here - you can get from London thru Las Vegas to Phoenix in as little as 13hrs. Sometimes thru LAX also. Either is an hour flight to Phoenix. Since you'd have to arrive a day early, there's both a Holiday Inn Express or Hilton near the Phoenix Airport - either is decent.
Rocio has a van shuttle from the Phoenix airport that takes guests directly to the boat on Saturday morning. Takes about 4 hrs., they cross the border at a minor entry point so there's usually no delay. $100 r/t IIRC. Most people diving with them do that.
Had it been winter, everything you want to see x10 would be at Socorros - their other destination. This late in summer all the Socorros trips have stopped. Those trips are also 10 days, $3K plus and sold out well in advance.
Afterward if you wanted to try one of your other choices, there are decent connections to Belize, Roatan or Cozumel from Phoenix. We can be on Roatan by noon, to Belize City by noon or Cozumel (direct not thru Cancun) by 3PM. All the flights leave at 5-6AM though so you'd have to overnite here on your return, I don't think the Rocio van gets back much before noon or later.
Sharks are a given on the
shark dive off Roatan. Probably the only ones you'll see there though. From my personal experience we saw fish but not huge schools of them. We mostly dove the north side. Saw a few big grouper, turtles everywhere. I'd really classify it as a macro destination. Since I like bigger things also, I was disappointed.