If you follow that last piece of advice about gunslinger/sniper, expect to die. A lot. They're mechanically complex classes (I think the Scoundrel/Operative are harder, myself) in lighter armour that do a lot of damage. Although the Smuggler storyline is great fun, and you'll have lots of opportunities to snark and flirt. Note that the Scoundrel has stealth, and can get past a lot of encounters without having to fight.
Sage/Sorcerer (Jedi Consular/Sith Inquisitor advanced classes, selected at level 10) are generally regarded as overpowered. The Consular storyline starts of quite interesting, from what I saw. The Knight didn't grab me, story-wise, though it does seem to be one a lot of people enjoy. Guardian is tough to kill, Sentinel is rather more a glass cannon. The Bounty Hunter is very tough, and I like the story up to 28. Powertech is close range melee, tank/dps, while Mercenaries are ranged DPS/healing - equivalent to the Republic Trooper Vanguard and Commando builds.