I would have to say at this point I like both WINTER SOLDIERS and BLACK SS. Every scenario played from those books has been close, tense and plenty of fun. I have most of the others but not getting a chance to play them, I can't be fair on my assessment.
Sinister Forces is a good read and I have played one from that one (the Scenario of the Month... Where'd that go?!?) that was OK.
Only have Dreadnoughts on the Naval side (GWAS) and haven't played that one yet so I guess that one is my favorite by default!