IA is my favorite. Got the warrior to 50 and then opted to level the other 7 classes in a rotation. On Quesh with them now. Every time I finish my rotation, I find myself wanting to go back to my IA and screw the rest. I'm already plotting another IA on another server once the characters I have are all 50. My current one is male so I plan to roll a female later. I wanted to see the Vector Hyllus romance more than anything since the guy rather intrigues me. I enjoy the other stories, too, but they haven't grabbed me as much as the IA has. If I had to pick a second best story, the trooper grabs me next. The rest are kind of equal to each other. I don't really hate any of them, but none of them really grab me as much. Thinking I may level another trooper, too. My current is male and I want to see the Aric Jorgen romance. Maybe I'll change my mind when everyone's 50 and I see the "ending" for each class. Time will tell. I'm rather excited to see where the story goes in the future for all the classes.
And with companion plots, Corso Riggs with a female smuggler I find to be hilarious. I can't flirt with anyone without him going, "Oh no, Captain." Then he goes off with a random comment like the guy being too old or not my type, etc. I also think Torian Cadera with a female bounty hunter is rather cute. I'm a touch turned off since he's often referred to as a kid, but the romance with him is quite amusing. The other plots for companions I find okay. I rather like Malavai Quinn although I'm wating to see how his story continues along with Lt. Pierce. Eventually the two are going to be stepping on each other. Pierce won't stay a lieutenant forever. Well, he could but wouldn't show much for the story evolving if he did ... at least without a good reason. Quinn could get promoted to Major at some point as well. Would also love to see Pierce and Quinn get into it if they're both being romanced by the player. Could lead to one of the two temporarily leaving the ship or something, although for that to work, it'd have to be within the Sith Warrior's story in general and not their personal stories so there's a trigger for the one who left to return. Also have to figure out how that'd work with a male warrior. Khem Val's continuation will be interesting especially given his "ending". Haven't really gotten too many of the other companions too far in their stories yet (or gone hunting for spoilers) to really know much else on them. So far the only companion I find to be a major pain in my backside is Ashara Zavros. Takes forever to get affection with her (especially for a female inquisitor), and half the time it's bugged. I supposedly get like 120 affection during her affection quests and yet get 0 at the end. Then I take her questing and get like 40 during the quest only to get 0 for that, too. Screw throwing the butler droids out the air lock. I'd toss her out.
I haven't really been this intrigued by a game in quite some time, especially not enough to be willing to replay the same class after having already played it once. I'm typically a "one time play through and I'm done" person.