I never actually got on with the TC4. The TC3 was a great chassis, and still is quite capable in the right hands. The TC4 was never really seemed to be as good (Or maybe others just caught up quicker). I remember the diffs needed a lot of attention, and the plastic axles would smash even if they looked at a corner marker.
The TT02S combines the best of the TT02 (efficient, light and robust drive train), and it also has the TRF / TA05ifs suspension, which is strong and handles well. Parts are also easy to get).