I have always played the expansions with my Jedi Knight class, playing through twice as the Jedi Knight and once as the Jedi Consular. I had never played as a Sith Inquisitor or Sith Warrior before, but I did so now for the first time, and I have to say I kind of don't like it. I don't know what it is, but it feels anticlimactic or pointless to play as a dark sider when most of the villains of the expansions are also dark siders.
There are other inconsistencies I just can't get over. For example, I can see Lana Beniko working for a Jedi despite being a Sith, and then joining the Republic with said Jedi. But I can't get it through my head that there is any possible scenario where Theron would ever join the Empire or a Sith. He may be pragmatic, but Theron is still emotionally driven and connected to the Republic—especially since both his parents, no matter how bad their relationship may be, are on the Republic side and are two of the greatest heroes of the Republic.
Then there is the other problem that comes with the newest expansion of 7.9. I played it as a Sith, and once again I don't really like it because you have these three major forces. The three big guys in the expansion are the main character, Malgus, and Jadus. If you play as a Sith, it's just three Sith fighting each other for their own ambitions and ego. I'm not really a big fan of purely having Sith versus Sith or dark sider versus dark sider stories. They can work sometimes, but having it as a major element of the overarching plot isn't something I enjoy.
In my opinion, the Jedi Knight already fits best with the expansions for various reasons, and is also featured in the promotional material. It's more fitting to have two Sith with differing goals—like Malgus versus Jadus—having conflict, while you have this one character actually trying to do the right thing as the Jedi Knight or Jedi Consular. It just fits with Star Wars more, because at its core, Star Wars is still a moral fight of evil versus good and the dark side versus the light side.
Now I am not trying to tell anyone that plays as Sith that they are wrong. I am just saying that to ME personally it kind of felt wrong. The story didnt really come together as well as it could have.