I think it comes down to what theatre/era interests you the most.
I also like the Falklands one quite a bit. The Argie early morning heli/airborne assault scenario is just such fun chaos.
I own Falklands (+ Feat of Arms), Nam, Red Star (+Days of Villainy and Bear and Jackal), Normandy (+Bastogne), and Pacific (+Hell Frozen Over).
I enjoy the Pacific setting but I'm not too keen on some of the special rules. The ninja stuff for the Japanese seems a bit overboard to me but I think that'd just because they threw in the ninja term. I suspect if they'd just called it "ambush", I would be less put off by it.
Red Star can be fun but given the lethality and range of modern armor, the maps can feel a bit too small and constrained in some of the scenarios.
Nam is good and there are tonnes of scenarios but the setting just isn't one that interests me as much as others.
Normandy is great. Wish they'd expand it a bit and add more Commonwealth stuff though.
I haven't played Bear and Jackal yet. We did try a few of the Days of Villainy scenarios out. Some interesting tactical choices given the crap nature of all the units but neither me nor my opponent could get that invested given that neither of us knew much about the Libyan civil war (and cared even less).
I did own North Africa but ended up selling that one. Terrain was too monotonous and the focus on the Italians rather than the DAK made it feel a but underwhelming.