My favorite story lines were with sith characters. Being a jedi on tython is incredibly boring. Being a sith on korriban and then dromund kaas was fun as hell. In terms of all around storyline and force abilities, I think the Sith Sorcerer was my favorite. I enjoyed playing as the Sith Warrior but I didn't know what a tank or DPS was at the time so I had messed up stats. It was much easier standing in the distance as a sith sorcerer and shooting lightning. At the same time, people were wondering why I was a tank/dpsed sith sorcerer.
Eventually I got good enough and joined a guild, then another one, to the point where we ran 4 ops weekly and finished everything first on the entire server (no credit to me obviously because I still sucked compared to the nerds). I think my last op was nightmare Denova. After like 5 times running it I woke up one day and uninstalled the game, never looked back.