The xxx-nt is more designed with the racer in mind. It's a little more fragile that the rc-10, but more tunable for driving. I don't have the rc-10, but I do have the xxx-nt. The rc-10 looks easier to work on. Things are more in the open. On the losi, everything is covered up in the middle by a chassis brace. It's a real pain when you crack a tank or want to replace the steering servo.
I can attest to the fact that the losi is a good truck, but I wish I had gotten the rc-10. I don't need racing tunability right off the bat. I just bash only. So the extra's that come on it weren't worth the extra $. I think the rc-10 is a bit cheaper as well.