I have both the TK10 and the TK11, but I never thought about buying any of the TA...
The TA30 is too large and heavy, I don't like the aggressive look, the TA20/21 are way to aggressive for me. I have other lights with a ring to change modes, that UI is really cool though and would be a reason to get a TA21, but not with that bezel and that ring design!
As for the TK, they are foolprof lights, perhaps they look boring and especially the TK11 isn't a beauty queen, but the lights have a more or less smooth design and are rugged as hell, you may use it as a hammer and it throws quite well (I have the R2 version). If I had none of them, I'd probably get the TK12 now... :thumbsup: