Voss and Imp. Taris are definitely good, as well as Corellia. Worst two for me were Republic Balmorra (the ending is dumb) and Hoth on either side, because the story is lame and copied to both sides. Everywhere you go, they're getting overrun by the opposite faction. Republic is probably worse since you know the imperials are basically laughing at them the whole time, while Republic is convinced they're going to win the war on Hoth. No, sorry, I don't think this superweapon is going to be different from the dozen we've already run into. It's not going to end the war however much you wish it so.
Republic Balmorra is really not that bad if you are a Consular since you