Well the Jammin is a nicer chassis than the Sportwerks, it handles better and such, but the included electronics are garbage (although the Rx pack and fail safe it comes with are a nice touch). Of course you've already got a XS3, so you've got that covered, pick up a decent steering servo and if you feel the need for more brakes you can replace the throttle servo. The engine on the Jammin from what I've heard isnt as good as the Mayhem's, but I can say the Force 26 I had was a great engine, decent power and its easy to tune/reliable. The included tires in the Jammin are pretty good as well. If you didnt already have a radio I'd say mabye to go with the Mayhem because of its included gear, but since you've already got it you ought to go for the buggy with the superior chassis. The Jammin is a super competitive buggy in kit/pro form and the RTR is basically almost the same car, just without as much fancy aluminum.carbon fiber. The Mayhem is a sport level car and doesn't have the same level of chassis design, plus the Jammin is less cash.