My Pick would be the Kyosho. Even though it's not without it's problems, It has had diff issues in the past (you need to be careful on how you shim the diff.). They do seen to have problems with the front hubs..I dont have any problems..I use King Headz hubs..
..The Xray has it's problems also..Shock pistons breaking is one of them I've seen..But for the most part both companies are dedicated to racing and both will try to fix any problems that come along.