Pulling Teeth, Poprocks and Coke, She's a Rebel, Basket Case, Minority, Warning, Letterbomb, Viva la Gloria!, etc. etc. etc. they're all too good.
Of course, I'm so barking up the wrong tree with that last song I listed. Nobody on the internet likes 21st Century Breakdown. It's one of those things people all seem to collectively hate. Some hate it for this reason, some hate it for that reason, some hate it simply because other people hate it. Like Nickleback.
Personally, I don't give a shit. If it sounds good, I'll listen to it. And pretty much everything Green Day has ever put out sounds good to me. If I had to pick an absolute favorite song though, it would probably be Poprocks and Coke. Understand it's excruciatingly hard for me to choose, but a lot of music requires me to be in a certain mood to listen to it, and Poprocks and Coke is the only universal song that I can want to listen to no matter how I'm feeling.