First off, after enough years in Canada, I like the idea of warm new years eve’s instead of some freezing crawl. I did Cuba last year and other than the return trip in Toronto, it went sweet.
I dont need clubs, the usual family type first night watching the fireworks will suffice, I expect only to stay a couple of nights, so I am getting ideas.
Declan
Typically warm. I’m about 45 minutes north, and usually wear shorts and a t-shirt to my regular outdoor party.
South Beach can be crowded and probably get crazy. Up near me, there are a bunch of fireworks displays in the Fort Lauderdale area - many cities do their own, and you can see a bunch at once if you are in a good location.
Honestly, if you aren’t looking for club scene, then Fort Lauderdale is just as warm, and a little less clubby. But I’m probably biased. 
Key West is a big party for NYE if you feel like the drive- I live in Key Largo and we usually just do local bar parties but you’ll find a lot going on in Miami and Ft Lauderdale for sure.