I have rode along side many of the quads people have mensioned here. the fastest one has to the 450 yamaha hands down. it out corners everthing with a good rider on it. the rapturd I was following in the tight stuff could barely pull away from from My Polaris Magnum 325 2x4(540lbs)+ me. the 400 ex is a great relieble quad if you don't muck with it. leave it alone and it will stay running forever. I have only delt with the DRZ 400 bike and not the LTZ quad, but they are very relieble. stay away from the single lever braking of Polaris quads if you can.(everyone elses left lever is rears only) if your not used it and jump on from another style machine it will cause you to flip on a down hill as did mine. packed me head first into a tree at 5 mph and destroied my knee.