This was the best season because the stakes were personal and not over the top, and this was also when the surprises were genuine, like when "The Sentinel" turned out not to be who he said he was. Mole #1 was a surprise (though Mole #2 was a sign of things to come).
I thought mole #1 was obvious. Nina had been mistaken for the mole so she was out. Tony was all too obviously not because he clashed with Jack all the time. But Jamie was the quiet innocent tech geek that tries not to draw too much attention that shows like this love to use. Allan York/Kevin Farrel was also obviously a baddie in my eyes. I saw the scene with Kim's friend coming a mile off. Mole #2/Nina was totally illogical and obviously made up on the fly as a last minute kool twist.