There are so many factors that go into this, that for me there is no single answer. Having said that, here it goes (from my experience) ...
Favorite boat: Aquacat. Very spacious and everything seems to be just where it needs to be.
Most luxurious boat: Nai'a (Fiji). It was a gorgeous boat.
Best atmosphere to make you feel "at home": Turks & Caicos Explorer. It may not be the most luxurious boat, but within minutes it will feel like it is your home and the crew are your family.
Best crew: Aquacat. I have been on her 5 times and so it is safe to say that the crew has turned over a few times, but without exception, they work tirelessly to give the appearance that everything is effortless, and they do it all while having a lot of fun. Kudos to the leadership within the organization to develop that in their crews. (The Turks & Caicos Explorer comes in a very close 2nd and must be mentioned.)
Best destination: This would be a toss-up. The weather was horrible the week I was in Fiji on the Nai'a and so it was not a good trip, but it was clear that even though my trip stunk that Fiji is an amazing destination. The other location would be the Socorro Islands off the west coast of Mexico.
Best Camera facilities: Nai'a. They have an entire room where you can store and work on your camera equipment.
Best food: No winner. In my experience, the food on every LOB I have been on has been very good.
Easiest Access (from Toronto): Tie. I can get non-stop flights from YYZ to either Nassau (Aquacat) or Provo (Turks & Caicos Explorer.
Overall Favorite: Just about every LOB I have been on (except one) has something about it that makes me think "I'd absolutely do it again." For me, the people on the boat make a world of difference, perhaps more than the boat or the crew or maybe even the destination. Keep in mind that you will be on the boat for a week or more and if you have a personality conflict with someone then you will be stuck in tight confines with that person until the trip is over. This can make or break a trip as much as any of the other factors. If, however, you are traveling with a great group of people, then it is hard to beat a week spent laughing even if other aspects of the trip "go sideways".