Kit has some metal upgrades. I bought the Dingo that is a kit. RTR is more convenient that you can just charge the battery and go play. I have all electronics; therefore i chose KIT.
The RTR uses AE-2 ESC which is a good ESC. The RTR servo is barely OK. The RTR radio is 2.4 that is ok too. IF you buy the RTR, just upgrade the front steering links. You will be good.
If you have never put a 1/10 RC Car Kit before, just buy RTR. Less headache= more fun times.