I was about to say the same thing as
@AggieDiver. Although I have never been to the Cayman Sister Islands in the winter, I have been there during the fall when there were high winds and choppy seas. I like both Brac and Little Cayman for similar and different reasons. I think that they both have nice features but Brac is usually the safer choice when the weather is rough because you'll have more options for diving on different sides of the island depending on the direction of the winds.
Little Cayman has the Bloody Bay Wall and it is spectacular and perhaps the best diving I've experienced in the Caribbean, but when it's too windy to dive BBW there are few other dive options around LC and they are just okay. I remember one trip to LC when it was quite windy and we spent a few days diving the south side and we were underwhelmed, but when we finally got out to BBW it was really choppy and the Dive Masters tied down the ladder for a few days to make it easier to get back on board.
There's also a bit more to see and do on land on Brac, and if you haven't dived the Russian Frigate (Tibbetts Wreck) that's a fun dive to do and there are plenty of other good dive options, too.
If the weather is nice, the CBBR dive op usually offers guests the option of spending a day off Little Cayman diving Bloody Bay Wall; while the LCBR dive op offers their divers the opportunity of traveling over to Brac to dive the Tibbetts Wreck - and a good time is usually had by all!
You can never be sure that the weather will cooperate, wherever you decide to go, but we've always enjoyed our stays at both of the Clearly Cayman resorts on Cayman Brac and Little Cayman because they offer great diving, excellent food, and nice people in beautiful locations.
Have a great trip to Brac!