I would research the tuners more if I were you. Everyone's needs are different.
I have had both the Predator and the Xcalibrator2. The user interface on the Predator is far better than the Xcal2. You get 5 lines of text on the screen with 6 buttons on the Predator. The Xcal2 has 2 lines of text and 4 buttons. Everyone brags about the support from SCT but check out their forums. There are quite a few unanswered questions and complaints. The product is still in its infancy stage. I wish it were more mature and stable like the Predator.
If you have an automatic, then the Xcal2 is a clear winner. You will get to adjust part throttle shift points and converter lock points. Well, someday. The converter lock points feature isn't working with their current release.
You can get a used Predator for around $250. As long as the previous owner set it back to stock, you'll be able to use it right away. A used Xcal2 is hard to find. New ones are still around $379. And if it's a 9400, you'll still need to purchase tunes from a dealer.
If you're just looking for a basic tuner, a used Predator would be my recommendation. If you think you'll get deeper into tuning, then I'd recommend the Xcal2.