R or J?

[Batfish]

The Jato is indeed a nice truck. I've now driven six different stadium trucks, mostly on the track, and I'd say that the stock jato can compete against any of them on any given day.
That said, driving a 2wd stadium truck doesn't compare to a 4wd monster truck.

All things considered, it should probably come down to what works better for your situation. If you're just going to bash, where do you bash? Street, park, baseball diamonds, parking lots = Jato. Trails, construction sites, rough terrain = Revo. If you're going to race, make sure the local track runs the class for the truck you're going to buy. If they don't run a monster truck class, you don't want to be stuck watching 1/10th stadium trucks race while you wait for track time with your Revo.
Of course, these are both nitro. Yes, the electric converted Revo (G2R) is coming out soon and, if I'd get off my butt and finish the motor mount, we might even have a more home-brewed conversion for the Jato :)

Either way, it comes down to what you're going to use it for that will determine which is more fun.