Hello and to answer your questions
1. For ROOs (both 42 and 44mm), look for JF made ones. For the FC or ceramic divers specifically, look for XF v2. For the stainless steel diver, I think that the best one is still the JF v7.
2. For differences, you need to do some research, but I have summarized your purchase decisions above.
3. The 42mm ROO is a bulky watch to wear due to the case design and also the lug angle. But you alone can decide what wears big and what wears small.
4. To my knowledge, there has been no 44mm diver produced. Even the old scuba model 15340ST was 42mm. If you do know of a 44mm, please share with the group, we can all learn something new.