Both cars are very capable, when set up properly. If you think about it, you're making the same adjustments on both cars to fix a similar handling issue - short of a few differences in the chassis and the top deck, you won't see many differences in getting either to perform well. XRay plastics, however, are far superior to those used by any other RC manufacturer - so durability tends to be far better as a result.
While XRay's "new car every year" concept irritates many drivers (probably to the point of frustrating drivers enough to leave on-road racing, or discouraging new drivers from getting involved; but that's a different argument altogether
), relatively few suspension and drivetrain parts have changed over the last few generations. You might buy the new chassis every year, but most of the common spares don't change from year to year.
Choose the car for which you're most able to get spares and set-up help; make the purchase from which you'll derive the most satisfaction, based on what you'd like to achieve. Do some research, and decide accordingly.