I use Trunks most.
Mostly because 1. I just like this character. I think he looks good, I like the sword, and I like the Animation of his main attack, the yellow beam
2. He seems to be quite strong in melee
3. You can transform very early
4. There doesn't appear a shining ball when charging his special beam/ball, what makes it better possible to attack people approaching you
Overall I just find him stylish
But I really dislike that his attacks, at least the yellow beam, doesn't seem to be any strong. But at least the Blue Ball seems to be quite strong.
Besides Trunks I also like Vegeta. I can't really mention technical advantages since I'm a noob to ESF (playing it since last saturday). But his beams seem to be very strong (final flash), and well, I like his look and the animations.
But this is just my opinion as a noob., so my fav. char could still change, since Trunks doesn't seem to be very strong overall.
[Edit]
Ow, well, sry if this isn't only technical, but also my opinion. But that's not that a big problem, is it? I just wrote down both