Definitely my favorite season. It breaks down to this: It's got the best +/-. Basically, the ratio of good episodes to bad episodes is through the roof. In fact, there's only two episodes this season that I really didn't like - Dead Man's Party and Helpless. And there are just so many good episodes this season, plus some unbelievable ones. Here's how I split them up:
BAD:
Dead Man's Party
Helpless
MEDIOCRE:
Anne
Revelations
GOOD:
Faith Hope and Trick
Homecoming
Band Candy
Gingerbread
Bad Girls
Consequences
Enemies
Earshot
Choices
The Prom
EXCELLENT:
Lover's Walk
The Wish
Amends
The Zeppo
Doppelgangland
Graduation Day 1
Graduation Day 2
Yeah, I honestly couldn't dream of a season that had a better episode breakdown. The percentage of excellent episodes is 32%. The closest season (IMO) is season 2, with 27%. Plus, there's the fact that season 2 has way more bad and mediocre episodes than season 3 does. I also happen to love the Mayor, he's one of my favorite BBEG's ever. And then there's Faith, and, as a Woz shipper, I have to love this season. And it's not just my favorite season of Buffy - It's my favorite season of any show, ever.
...Firefly was a close second, and Angel s5 was an even closer third.