I've lived in SC my whole life, so I am quite used to heat and humidity to say the least haha.
In regard to RSD, I definitely prefer heat over cold. I can't bear to touch ice, and my circulation isn't so great already due to the RSD, so cold weather makes it worse. Also, my flares are more frequent in cold weather. Even though I enjoy the heat, I have to be careful with the heat though because I don't feel heat all that well (circulation and RSD), and I already had a massive reaction to the heat a few years ago that sent my RSD into overdrive for quite awhile. But yeah, definitely heat over cold! Of course, if the weather is right in between hot and cold (70s or low 80s), I'm quite content as well.