Depends on wether you want to learn the art riding trials or just potter around on the easy course for a bit of fun. If you want to develop skills go for a smaller engine as this will make you use your body more and learn different techniques, where as a larger engine capacity bike will just pull you around anywhere, hence not needing as much effort and technique. Im 12 stone and rode a 200 for a couple of years and found it to be a very good, competitive bike, although most people will say that they are too flat don't listen as they are good enough for any decent clubman rider and will enhance your skills.
