TK's can do quite allright, the only reason ppl tend not tp play them is due to the facts that other tanks are stronger in pvp(offensive atleast).
that said a well played TK is extramly hard to kill as they are one if not the stronges tank in the game, TK do good in pvp but they arent a killing machine, so if you have played TK in the past and you enjoy it there is no reason why not to go for it.
Alot of ppl dont see the value in a defensive tank why? i dunno maybe they never met a good one and therefor belive they are weak this isent the case.
remember in the end it comes down to what you prefere to play and not what ppl think, its your time so pick a class you enjoy or your just gonna quit in a few weeks.
and i have to agree with modoy: but saying TK is useless just because u cannot get hero is pathetic imo.