For me, the best Oasis song in the world is still "Supersonic". That song just fuckin' RAWKS
, no excuses. Now I'll admit that a) I've only heard one of their albums all the way through (Heathen Chemistry
) (but I'm willing to hear more), and b) my one and only Oasis collection in my possesion is the silver-boxed EP collection for the UK singles from the first CD. That said, I've been a bit underwhelmed by most of what I've heard on the radio, including (sadly) "Wonderwall". That one more than most will forever suffer from penultimate overexposure more than anything. But for me, the problem with Oasis is that they were a great band on paper, but ultimately only reached the brass ring a few times. But that's just my personal taste; your mileage may definitely vary.
The coolest Oasis release is the EP Wibbling Rivalry
, a spoken-word interview/fight that the two of them gave. They're both pissed at each other, and they're really giving each other the business