I ride quadbikes, brothers all race. (ace sport) i would suggest a Bombardier Outlander 800, or a grizzly it will pull anything. and last for ever.
ANY quad related question visit
www.quadheaven.com
Please do not buy a Chinese import, 250cc thing on the road, all other quadbikers will laugh at you, sort of like a paintballer in camo's wielding a tippman custom. The imports rust and start to degrade after a month or 2.
When you get your quadbike OTR the MOT place have to restricted your quadbike to 12HP, this can be easily combated by taking off the throttle cover (on handlebars) and taking out the nut or screw they have put in there, cops haven't been trained to check this sort of stuff on quadbikes so won't know the wiser.