If terrorism still means to terrorise populations (the term has now become so hackneyed that this is by no means a semantic certainty any longer) then it is arguable that governments, rather than disaffected factions, are by far the more frequent, the more effective, and the most adept at employing it as a political tool.
"Rebel" as a chiefly positive connotation of political activism is also rather a modern take on the term. Perhaps the Star Wars film franchise is to blame. When Britain, even in its own military language of the day, executed the rebels who led the 1916 insurgency in Ireland I do not believe they were boasting about killing the "good guys". So for me this term also is now hackneyed to the point of obsolescence.
"Freedom fighters" retains some semantic clarity, even today, and even in terms of political double-speak. However it is rarely employed with an accompanying clarification regarding the nature of either the "freedom" to which the fighter aspires or of the manner of "fight" they will use to achieve it. Upon closer examination therefore this term, used to envelop so many who would also fit the hackneyed but seemingly popular use of the other two phrases mentioned, shows that its apparent semantic clarity in no way reflects any other kind of clarity in its use.
Gil is correct above. The terms are only useful in gauging the political nature and stance of the government or media organ that promotes their use. They are absolutely worthless in gauging the same for those who the terms purport to describe.