Pshaw to the 4, with its posh posturing and smiling drivers. Nuts to the 16, with its two-car buses choked with scholars en route to the U. If you want to ride a bus and get somewhere, it's the 21 or nothing, the bus line that's about the journey as much as the destination. The stalwart straight line that connects south Minneapolis to downtown St. Paul takes you about as far as you could hope to go without snatching a transfer (and if you're one of those who needs to get from Spyhouse to the Turf Club, this is your only option that doesn't have yellow checkers). But it's the ambience of the 21 that puts this bus line a head above. The closest thing the Twin Cities has to the L in the Big Apple, the 21 is pure utility spiked with harrowing humanity. Go the whole way, stand before the majestic Capitol dome, and you too will be able to sneeze at every other bus line in town. There can be only one.