if a liveaboard I would go to the Turks and Caicos without hesitation over the Saba, St Kitts route. While the diving off of Saba was great...St Kitts was not nearly as good. So depending on where you start on that trip (either St Maarten or St Kitts) you will only really dive Saba for 2-3 days. We actually got delayed in St Maarten due to weather and dove there the first day. the diving in St Maarten was not worth doing (at least where we went).
the Explorer boat that does the Saba/St Kitts trip needs to be retired. It is old, loud and not well set up. I also though the crew was a bit lacking. While one of the DMs (Claire) was extremely nice and helpful, the rest of the crew made it as if they were doing us a favor by diving off of their boat. I thought that the purser (Lynn) had an attitude problem and the captain (Ian) had zero personality and needed to learn how to smile.
I would not do the liveaboard in Saba/St Kitts ever again...but I would go back to Saba in a heartbeat. The diving there was very good and the island has a great feel/charm to it.
In contrast...I would go on the T&C Aggressor again. The boat was spotless, the food was good and the crew were all excellent without exception. Hope that helps.