Best kent theme parks?

for my b day i wanted to go to a theme park, i was thinking chessington, but is this a good choice? thorpe park is to water themed and thrilling for me, i was thinking of going before the school holidays ( so it wont be crowded ), my b day is on the 25th july, or is there another better theme park around kent? somewhere that has not so thrilling rides, like chessignons "runaway train" and stuff like that...