Here's my opinions on each of the companions, along with a very brief reason as to why on each:
Anders: -2 Simply because BW took the cheese dick route and brought him back from the dead just like Leliana. I liked Anders before this happened.
Avaline: +1 Even though she seems like a "girl scout" at times, at least she didnt seem to constantly shove it down my throat how I should be exactly like her. She's just enough girl scout for me to be ok with it.
Bethany: 0 Pretty indifferent to Bethany. Dont know why, just am. Probably because I havent gotten to play enough with her since Ive had to put my game down while waiting for the damn console patch *taps foot impatiently* lol
Carver: -2 Simply because no matter what you do it seems, you cant get this guy to like you. Reminds me alot of Korn's lead singer for some reason with all the whining, pissing, and moaning he does about being in Hawke's shadow and jealous of him.
Fenris: +1 Because Im pretty broody myself at times so I can kinda relate
Isabela: -1 It would have been a +1 instead but after that scene at Ander's clinic where she's being apparently cured of some what I assume to be some venirile disease she's picked up from being so oversexed lol.
Merill: +2 Because she's cute, awkward, and has some pretty witty one liners IMO. What's not to love?
Sebastian: -2 Only because there isnt an option for me to use anything worse than a -2. Had I the option I'd give him a -10 because he's a male version of Leliana and just as preachy.
Varric: +2 Im usually not a big fan of dwarves. But the way Varric was written, he is definately an exception. Easily my favorite companion, period.