This is how I think....
Galak pwns Zett, he is to young to defeat him.
Galak then proceeds to own Han, because Han's blaster cannot go through his shields.
Then it is Alpha, who could probably hold out pretty long, but will lack the fire power to get through. And he cannot dodge rocket launchers....
Obi-Wan could possibly win this, but that depends on how long he can deflect the imperial repeater, how long it will take for him to cut through the shields, and if he can react to every single rocket shot. I think Obi would have a hard time with him, I'd give Galak 6/5 to win....
Boba has alot of explosives, and his jet pack would make him good against explosives and would be harder to hit. Boba could possibly blow up the shield, but Galak still has armor underneath, and the shield reloads after about 10 seconds. Boba has a good chance....
Grievous, I think, doesn't have anything that is very effective against Galak. Can he dodge rockets and deflect high rate blaster fire for a long time? If he strikes the shields so they get down then he has a chance. I think it depends on how fast he gets close....
I'd say Galak has a chance to get through....