To me, The Pumpkins put out 4 brilliant albums basically one after the other and that's enough to put them atop my list. Pearl Jam has been the band with the most longevity. Nirvana and AIC both come with a large "what if" factor though.
Hard choice between Pearl Jam, Smashing Pumpkins and Nirvana. But I voted for PJ because they had more longevity, despite egos, hard drug addiction and whatnot they kept it together, unlike the Pumpkins. Also, I think from 2000-2003 they were one of the best live bands ever. When they were tight and locked in its hard to think of anyone that compares.
I saw the Pumpkins on the Zeitgeist tour and Billy was -blam!-ing unbelievable but it didn't seem like The Smashing Pumpkins.
And Pearl Jam treats their fans really well. What other band would take Ticket Master to Congress? Plus they do they so much that goes unreported like a year or two ago they built 1 skate park a month for a year in poor areas around the country and give a lot of money themselves.