I'm not sure I understand your question. Are you talking about limited time on the vacation?
When I went to Belize, I dove the Blue Hole. That dive in itself is a BTDT dive. There's really nothing to see. The caverns are too dark. You basically descend, swim through the cavern, and ascend. The only thrill was seeing the outlines of the Bull Sharks about 30 feet away, but it was really too dark to see much else.
What makes this trip worth it is the wall dives afterwards. If you're diving off Ambergis, you'll see decent reefs, but not great reefs. These reefs are open to the sea, visited a lot, and the walls don't start until you reach 100+ feet, and the dive guides don't want anyone going below 80 feet there anyway. The walls further south around the smaller cayes start at 30-40 feet and have lots of coral and sponges. These sites are pristine. They are protected and not visited as frequently. These dives alone make it worth the ride out.
So, if forced to choose one of your responses, I'd choose the 3rd one. However, I can't say I regret diving the Blue Hole in and of itself. It was a different experience, nothing to really see, but I can say I've been there.