Might not be the best person to ask for an opinion on humidity/heat because the heat has never bothered me. I just use a ceiling fan and open window all year long.
Not sure what you like to do, but St. petersburg's downtown has some great fine/dine culture a couple museums good food. Not much of the way of alternative/freak culture but it's here just small. Tampa has a lot more burning man type culture, but a bit more big city like. 5 free great clubs downtown all within walking distance of each other if you like dancing and or hooking up. You have water alll around you. Beach after beach. The tropical wildlife is probably my favorite thing. Always makes me smile when some random big a$$ tropical bird decides to say hello.