SOME SPOILERS
Season one is definitley a tie for Torment of Tantalus, and There but for the Grace of God, I think Catherine is an excellent character, and would like to see more of her, also the history of the gate was fascinating.
Season two is hands down, no competition Matter of Time, some of the most amazing special effects, and an awsome story both in the same package!
Season three I have not seen a whole lot of, but I think it was called Rules of Engagment that I liked alot.
Season four had an excellent episode with Upgrades, but I think the amount of freedom, and expression that was developed in Window of Opportunity made this my favorite episode of the series so far, RDA also had a nice bit of acting at the end when talking about the loss of his son, pretty convincing, and was also a just plain fun one to watch!
Season five - So far everyone likes Threshold, I thought it was okay, but I liked the background information about Teal'c and Bratak in Enemies (I think it was called) But I have to be the oddball here, and vote for the latest episode Red Sky, I know the whole pilgrimesque setting was a bit boring, but when that guy got some of Jack's men killed I thought that was some of the best acting I have seen out of RDA yet! While he is a witty guy I like to see him get pissed off like that, a real leader would have in that situation. I remember watching him darn near knock the guy out, and then drew his Berreta on him, I was thinking go Jack, go! I really like seeing Jack, and Hammond assume thier authority when they need to, they both portray it very well. Hopefully we will see more of this from RDA, he can actually do drama pretty dang well, and I'd like to see more of it!