The Sith Empire

The Sith Empire is currently much larger than The Republic, which is in a dark age. Most of the Sith are too consumed with infighting between the different clans and the Sith Lords sitting on the Council of Thirteen to spend much time going after the Republic, and as such the Republic seems to be slowly turning the tide.

In Terms of the Heroes
The Sith Empire has currently put a fairly high bounty on the heroes head due to their dealings with The Republic, and the death of Darth Homunculus