The only reason I didn't mention the tb-03 is that it is essentially a digital(software) option, whereas the TT-03 is still analog. I still think it sounds pretty good.
The TT-303, on the other hand, despite being "circuit identical", can sound downright weird at times (as can Roland's other "analog modeling" 303 reproduction, the TB-3)
Here is a 4 way comparison of the 4 synths I just mentioned complete with waveform visualizations: