X-Ray is not the thoughest car, that is not true. I see regularly people breaking them, especially C-Hubs and rear shock towers. What was true for the pivot ball car is no longer with the plastic C-Hub version. It IS tough, but no the thoughest.
Having raced TRF 414's for more than 2 years, and partecipated to tamiya euro cup for the same time, I have to say the TRF series are very very durable. In 2 years, broke a front wishbone and an outdrive (in the same crash, wishbone broke and the dogbone took the delrin outdrive with it, what love can do
). The crash was just a car full speed hiitting my stopped car just on the worst position you can imagine for the wishbone. Hell it bent my Ti turnbuckle !
The Assassin is very fragile, especially the wishbones (why do you think they released alloy wishbones ? An error IMHO as instead of breaking they'll just bend).
The SD is better now with the upgraded parts, but not really tough, I'd say it's ok now.
The Mi 2 breaks wishbones easily, I saw it several times.
The pro4 is Ok, but still breaks wishbones, i just saw loads of them break.
Losi... Well I prefer not think about it, my mate just changed to an SD because he was fed up with repairing the car.
Can't really tell about the others, as they are not popular where I race, but my vote definately goes to Tamiya !