Actually, I can't decide between Silent Thread Reborn and Inferno. Since the first is fully released, I guess it wins.
Both campaigns don't depart from the classic Freespace formula and story telling, something both Derelict and Blue Planet do.
Also, I consider Derelict's mission design (especially everything that involves pirates) somewhat weak. It IS a great campaign but the level of quality shifts somewhat. Blue Planet wins originality but I am just in the "Freespace 3, please!" camp here.
STR gets my vote.
Somebody needs to start a TBP campaign poll too here. I can't do it, I am biased.