I have four 50s, five if you count the one I deleted: Trooper, smuggler, inquisitor, agent, warrior (deleted because I ****ed up his story and I never finished his Act III). I also have a Knight at L40 and a Sage at L33. I got a Bounty Hunter to L30-ish but deleted him because I didn't like how I made him look (I actually did this twice and have rerolled a third one which is at level 23 right now.).
First off, the trooper and inquisitor storyline give me no wish to replay them at all. The trooper story after Act I was just dull and any threat was pretty far off and disconnected from your job - there wasn't even a real antagonist besides 'the empire'. I played it lightside the first time, and the idea of playing it darkside actually makes me cringe because no amount of twists from going darkside could make it more interesting.
Insofar as the Inquisitor goes, I've heard that the lightside story really sucks and makes almost no sense, and the darkside one wasn't that great either - it had a great ending and a whole lot of Crowning Moments of Bad_ss, but that's about it for its redeeming qualities.
The smuggler storyline, which I did lightside, was interesting enough to, well, keep me interested, though the Act III plot twist ticked me off. I'd like to go through it again as a darkside smuggler, but I'm not sure the story by itself could keep me interested because it was pretty 'meh' - average as these things go.
The Agent and Warrior storylines, on the other hand, were fantastic (with the Agent by far being the best on in the game thus far - I don't think anything in this game could possibly outdo the end of the Agent's Act I.); I'd love to go through an Agent again with a darkside twist. That one twist actually changes a whole lot of how you experience the story and is really freaking awesome, and your character is incredibly differently portrayed from there on out.
For the Warrior, I made a mistake here: I went darkside up to Tatooine, but a cutscene managed to convince me to change (slowly) to lightside. I decided that I didn't like this very much and ended up deleting the character. The story, though, is great: your actions matter, and if you play it right there are a whole lot of Crowning Moments of Bad_ss. The most memorable moment for me is where, if you do some maneuvering and settle for some lightside points on Nar Shaddaa, you totally out-maneuver your enemy in a style true to a sense of classic, ruthless Sith cunning. This is definitely a story worth playing through lightside and darkside.
The Sage story is boring as hell. Really boring. I haven't finished Act I, though, so for all I know it gets better. It's also notable that this is my third Sage reroll because I didn't like the way the character looked.
The Knight storyline is interesting-ish (this is my third Knight reroll, which I've decided to stick with) and has a lot of differences, from what I can tell, if you replay it darkside versus lightside. It's pretty freakin' cool. Worth replaying.
The Bounty Hunter storyline so far seems very interesting, but I never finished Act I so I never actually saw the full thing. It's got this great attitude where you're this freelancing, greedy bad_ss who can pretty much get away with anything - if I wasn't on my third iteration it would be almost sickeningly fun to play.
In a level of fun-to-tedious, I'd say it's:
Tier 1 ('Great' to 'Blew me away, amazing in every way'): Agent, warrior, bounty hunter, knight with the Agent coming out on top by far
Tier 2 ('Captured my attention' to 'above the par"): Smuggler, inquisitor
Tier 3 ('worth playing through' to 'not all that bad'): Trooper, Sage
Edit: Some people said that the Agent story was the most boring and implied that it had a really small scope. This is really confusing to me, because the Agent story is by far the most epic-in-scope story in the entire game - it makes the Knight and Warrior stories seem like nothing they did was a big deal (and I know what the endings are for both of those.).
The Agent story is one of those very few things where I left it inspired and hoping that I could write something with that kind of quality, and I'm the guy who went through the Trooper storyline thinking about how much better I could've done it (I'm not the best director, so I might not be able to do it better, but at least my imagination has a vision with potential that far outweighs what we actually got.). I also think Inception is a 'meh' movie because I am an incredible critic.
Edit #2: I'm the guildmaster of a Republic guild, and I just said the Imperial stories were essentially all better than the Republic ones. This is a great way to get recruits. XD