Here's my ranking:
1. Season 3 - As much as it hurt to have Jim and Pam far apart, this season was really my favorite by far. I can't even think of any episode in Season 3 I didn't like. The merging of the branches was great, seeing Pam come out of her shell was amazing, and you just can't beat Michael standing on the roof, yelling "Dwight, you ignorant slut!"

2. Season 2 - As Papa said, this was where the series was able to split from the UK version and establish itself as its own entity. There were some great classic episodes and some amazing pranks, but I still hate seeing Jim pining for the girl he can't have. Somehow, its not as bad watching Pam pine for him, because I know he still loves her.

3. Season 4 - Has had a few falters and some of the hour long episodes dragged on, but Michael hitting Meredith, driving into a lake, and of course, lots of JAM action make it a pretty great season so far. Branch Wars and The Deposition really stand out.

4. Season 1 - Short season, and I wasn't terribly fond of The Pilot or Basketball. But Health Care is one of my top favorite episodes.

Season 3: this is when the show really came on to its own, and i love ANDY!! the story lines were always strong.

Season 2: i agree with you two about this one.

Season 4: i really like this season so far its not over yet (though it very well might be!) im pretty sure if they add some more epi's it will be my number 2.

Season 1: i watched it from the day the pilot premiered it was good but i think it was too similar to the brit version!

Season 2: There was a Huge Build to all the Charcters. We Learn a Ton of things! etc. Michael's Man Crush on Ryan, Michael is obsessed with become a Secret Agent and We learn Pam has Feelings for Jim! Favourites: the Injury, The Client and Drug Testin. Great Scenes: All the Pranks and Jim's Confession.

Season 3: We get to learn about new Charcters including an Evil One. We fall more and more in Love with Jam also there was a lot of Romance. Great Episodes: Safety Training, Negotition, Beach Games, Gay Wich Hunt and Product Recall. Good Scenes: Faxes from the Future, Jim imitating Dwight and the Michael's "Secret" Romance.

Season 4: Even Though we are Barly throught the Season it has been a Great Season. With Random Kisses, Computer Talks Back and Fake Moustches! Great Episodes: Money, Branch Wars and Dunder Mifflin Infiniry.

Season 1: The Only Reason it is Last because it has 6 Episodes. All the Episodes are Good Besides the Pilot. Favourite Scenes: Basketball, Alliance meeting in the Warehouse and Mr. Brown. Favourite Episodes: All of Them Besides the Pilot.

I Love all the Seasons!

I'm same as chel1395 with my order:

Season 3: There was so much going on this season. There were two branches, more characters, some AWESOME quotes, and better romance. There was more depth to the show, and that was nice to see. Favorite episodes: The Job (obviously!), Benihana Christmas Special, Back from Vacation, Safety Training

Season 2: This is when we REALLY start to get to know the characters, because season 1 didn't do such a great job. But, I loved seeing all the characters grow and develop, and the show taking some kind of shape.
Favorite episodes: Office Olympics, Sexual Harassment, The Injury (duh! :D) and Drug Testing

Season 4: What a shame this season was cut short, because I was really looking forward to the new stuff. I read on Jenna Fischer's Myspace (don't have one myself though) that the episode they were currently shooting (before production ending) was probably the funniest of the season, and that's a real bummer. I really like this season, but something seems to be missing. And I don't think it's that JAM is finally together. I just can't put my finger on it.
Favorite episodes: Money, Branch Wars, The Deposition, all funny ones.

Season 1: This season got off to a slow start with the pilot. And the fact that it's the shortest doesn't help its cause. We just couldn't get a good enough look at everybody, they even had some errors (Meredith is not an accountant, as said in The Alliance). Even so, they had some good episodes.
Favorite episodes: Health Care (just for the "lion" monologue), The Alliance, Diversity Day

1. Season 2 - I could (and I do) watch this season over and over again. I can some it up in this sentence: "I miss Ol' Pammy."

2. Season 4 - Even though it's been short and the shock of the writer's strike frightened me, I still find it hilarious. I guess it's mainly because of the hour-longs and a whoppin' two Mose sighting in a span of five episodes.

3. Season 3 - Not so good, in my opinion. I don't like Karen.

4. Season 1 - Even though it was hilarious it must end up here due to it's short length.