I've had great luck as far as durability goes with a Slash and Rustler, at least once i swapped out the radios. I would definitely go for 4wd though, so much easier for my son to drive than 2wd vehicles.
If i was going to buy a truck for my son specifically, would likely be the 4x4 Slash. He has a RedCat equivalent that is not bad at all, but not as tough as the Slash has been. My rustler has had about the same amount of broken parts as the Redcat, mainly due to the large wheels sticking out at all 4 corners....slash you get a bit more protection.