Was there last year, late Nov/early Dec for a week
Weather was fairly ok, only 1 really bad day so hired a car, volcano stuff is cool.
Most days had a few hours of sun, it was generally pleasant all the time, - take a jumper/fleece out at night
Didnt go in for much nightlife but I think it wasnt bad, fairly late starting - after 12am - after a feed and a good bit of wine would be heading for nap by then ....
Puerto del Carmen seems the best and the old town part has a bit of charachter (well, its all relative). Decent standard of place, no high rise, not much in-ya-face ENGERLAND stuff.
Other resorts on the island looked really really quiet - and the main town, not a touristy town, called Puerto Rico if I remember right (no, not the US territory) looks uninteresting/dodge so I wouldnt be bothering with that. El golfo on the west coast is nice for a bit of seafood but I wouldnt think you'd spend too much time there