2 light sabers will always be better than one. for example, if i have two light sabers, i can stab one thing and then stab another at the same time. or, i can stab one thing and then stab the same thing immediately afterwards without delay. i can also block two blaster fire at the same time whereas with one light saber i can only block one at a time. with two light sabers i can also look much cooler.
tl;dr 2 light sabers > 1 light saber.