Tricky question due that both are helpful depending on the situation. The fighter will have to die in order to have the possibility to revive, in the other hand the rogue class gives you the possibility to stay alive longer which is helpful before her special goes off but if her special in on effect and she dodges, she will not counter because she would not take any damage, the other heroes next to her will but not her.
Counterattack is used in its full potential when you are facing heroes that hit multiple so the damage inflicted to themselves becomes fatal. Everything will depends on your strategy on a particular battle
if you chose the costume path you will get the costume bonus and you will have to level the regular one as well so you can go back and forward as you please