The question is in the title. Here's my pick:
Lando Calrissian:
"During the perform action step, if you are unstressed, instead of performing an action you may roll an attack dice. On a crit, hit, or focus result you may perform each action listed on your action bar."
I do understand the theme behind Lando's current ability. He was the squadron leader during the attack through the Deathstar II's 'trench', so he has a leadership ability that pairs well with his copilot Nien Numb. It's just a bit meh for such a cool character.
This new ability, much like his crew version, focuses on Lando's gambler nature giving a 6/8 chance of being able to perform 2+ actions per turn, brilliant! As with all gambles though there's a chance you lose out, getting no actions at all. Obviously this pairs well with the old MF title and engine upgrade to add more actions to your action bar. Recon is also great to grab you multiple focus tokens.
Normally I don't like random abilities too much, but in this instance I think it's appropriate. Skewing a great ability towards success makes it more playable than some of the other RNG effects that are 50:50 for weak/OK abilites.
What unused pilot would you buff?