SW - Broonmark is utterly useless. I forgot why he is still with me. Whatever, good parking lot for my old gear.
BH: Apparently everyone hates Skadge, I haven't gotten that far but I watched my friend get him and he seemed funny at the time, so idk...
JK - I didn't even get a chance to use Rusk before I got Scourge, so he never even had a moment of use. Probably the most useless companion ever, but he's kinda cool as a person I guess. Also, T3 is just a signature astromech R2-D2 replica that has a completely uninteresting story that I almost just want to space bar through.
Sm - obviously the signature Chewbacca/Zaalbar ripoff, Bowdaar. Oh my freaking god all he does is complain about slavery. Kind of reminds me of real... never mind.
Tr - The Gand guy is annoying and ugly, stupid bug people suck!! In fact most of the companions for Trooper seem kinda tossed in without much thought. I absolutely LOVE Elara though (and she loves me ). Jorgan is... interesting enough.
The rest of the classes I haven't played enough to judge accurately but Khem Val is only cool after Act I, I know that much...