I think your looking at 4 excellent rigs in your line up....however...the reports that I'm reading about the Rustler is that it is very fast and hard to keep the front wheels on the ground. I'm sure your 10 year old would love to see his rig doing wheelies but at his age...maybe with less driving skills...he would not be that pleased at the overall results.

I have both the RC10GT and the XXX-NT and I really like them both. I tend to gravitate toward the XXX-NT due to the better radio and the "extra" details that are built into this rig.

I also have the HPI MT 4x4 and it also is another good rig....in my opinion....and I think it would handle well for him based on his age. With the crummy weather we have had I have not even had my rigs off-road with the exception of my TMaxx and that is not in your line up....so I can only really offer you advice about on-road conditions. I like them all....and I'm sure you'll pick a winner for his age.

Good Luck!