The RXT and GTX Limited are essentially the same three seater PWC. The GTX has some extra features, GPS, Depth gauge, and tilt steering* (The International RXT also has tilt steering while the U.S. RXT does not). Both weigh roughly the same, the GTX Li is more expensive due to the extra features.
The RXP beats both crafts off the line and in top speed, however you sacrifice a seat. It is a smaller craft, not as great as the larger crafts in chop but it will still handle wake decently. It also features a V.T.S. (trim system) unlike the RXT and GTX Li. However, if you have the cash and patience, the new RXT-X and RXP-X have 255hp and both also feature V.T.S., very useful on all PWC's.