B4/T4 for sure but i havent driven the kyosho rb5 yet, it looks really good.
The 501x buggy is hella strong too and performs very very good, the only time i saw one break and i think it may have been a fluke and it was a right rear axle, but the hot bodies rear axle fit with some shimming and it looks like it would be stronger. And you would have a good chance of finding one of them at your LHS