On multi- vs. single-channel amps
Multiple channels give you "versatility", but with that comes complexity. It's easier and quicker to set up one channel than multiple channels. With multiple channels, you have to worry about balancing tones and volumes among the channels. Higher-gain channels compress more, so their volume settings are most likely to be out of whack as the band gets louder or softer. Modest changes of your guitar's volume pot will affect the clean channel more than the distortion channel, so there's another juggling act going on. Try to fix it with a volume pedal in the loop, and you've got one more variable to juggle (in addition to playing, of course).
On the other hand, a single channel amp is a one trick pony. Or is it? The amp does just one thing, but the guitar (and the player) can do a lot. You've got the tone and volume controls on the guitar and your playing technique, all of which can have a dramatic effect on the way the amp sounds and on the way your sound fits the band's mix. A slight change in picking intensity can pull your sound forward or back in the mix. Dig in harder for a solo - depending on the amp your sound gets louder or compressed and distorted.