well if the person is going to be a tank i would say healer so Jedi sage, commando or Scoundrel would be good.
But i would like to say play the class that you want to play it would be more fun for you
i have Tholomew-Plague as mine and i love it but i do think that you should be able to change it like 1 for free then after that cost or just 1 time then no more