That was a really hard choice I haven't actually seen all of season 4 just clips and the last couple episodes,
Season 1 I just love because you get to see her liveing the double life and its truly the good old Days, Francie & Will, meeting in the garage, rambaldi is first introduced McKennas Cole, Anna, Sark, Dixon and Syd on missions, and theres just some great aspects of season 1
Season 3 is Fantastic!!!! I loved the Drama, I'll admit the first time I saw it (on DVD) I was like crying for the first 4 episoes and ny the middle of the 5th I had stopped, but then I cried during the ending with Lauren kissing Vaughn in the hospital, and then I also cried during concious where she had the ream where vaughn was never married and she finally tells him stht she loves him but it was just a ream. But when we learned lauren was evil it was just so much more fun you just couldn't wait until vaughn found out. The second time I watched it it was fun because you know what happens and stuff and just enjoy it so much more.
and you love ppl like marshall, Wiess, and even sloane who still all know that s/v are still in love. But the first time seeing it is always the best because you just have the feel of the drama.
But in the end I'll have to say season two. The great lines in The enemy walks in, the great episode where sd-6 is destroyed. Lena is great I just love her, and of corse the cutest romance ever Syd and Vaughn even though phase one is there first kiss I truly think counteragent is one of the best s/v episodes ever, because its where we really know for sure that Syd is in love with vaughn, the way she looked at him over the hospital bed, and Irina is just ausome in that episode. And then the family moments in Passage, god I just love season 2.