I do all three synbyn. Fringe at Sidfmouth and Whitby. Performer at Broadstairs. All three entirely different from each other. Broadstairs has the best social side by a long chalk.
Sidmouth seems to roll up the pavements at midnight.
Whitby is fine if you're locked in.
Broadstairs is the only place you can party and play until dawn every night under cover and without disturbing campers and local residents.