I have not done any of those, but have talked with several people who have.
All 3 liveaboards get great diving reviews.
I was told by someone not to go to Saba land-based, it is too much of a hassle to and from, and you waste too much time. The diving by the guy who went land-based is very hard to please. He said the diving was good. The best diving he did in Carib was from Cayman Brac, he says, and is only place in Carib he would return.
Several people I know have done the Cayman Aggressor and absolutely love it.
A few friends have done Little Cayman Resort and feel the say way about it. I have been discouraged from going to Grand Cayman due to tourists and too many newbie divers.
I don't know anyone personally who has done the T&C Aggressor or Explorer boats, but I have read several reviews. All enjoyed them, but I don't know if they are any better than Cayman Aggressor as from what I read all the dive sites for T&C are very similar, Caymans gets you more variety.
As I have said, I haven't done any of the 3, but would love to do them! They all sound fantastic. And if given the choice... I would do them from a liveaboard, not land-based.
robin