On channels... to switch or not?
If you need sudden jumps in gain - clean, crunch, saturated - during a song, then you kind of have to go with a channel switcher. Especially if your tones are dictated by a recording, as they are when you're in a cover band that's trying to be authentic... There's no limitations on what the artists can do in the studio - many times when you think there's a channel switcher involved in a recording it's actually a change of (possibly) amp, guitar, effects, mic positions, even the guitarist.
My opinion regarding channel switchers has gradually changed over the past few years. At first, I really wanted the "flexibility" of a three-channel amp. Then - as my ear became better educated - I realized that there are compromises in the sounds of a multi-channel amp. And problems balancing levels among channels so all the sounds fit the mix (particularly tough when the band plays with a lot of dynamics). Let's not forget the joy of trying to sing and play guitar and hit the proper footswitch(es).
Eventually I started using the channels less and less. At first, I'd just use one channel for an entire song, varying tones with the guitar's controls. Later, I started settling on one channel for everything, still using the guitar's controls and playing dynamics to change the sound. My playing style evolved along with the change in amp use - leads became cleaner, and I relied more on volume for sustain. (That had the added benefit of being able to do controlled feedback and bring out harmonic overtones.)
At this point, my first single-channel amp was a revelation. These tend to be set up so everything starts to distort at more or less the same time: preamp, PI, power tubes and speaker. That typically brings in a lot more character than in a channel-switcher where the power amp and speaker tend to be set up for clean playing, leaving most of the distortion generation to the preamp tubes.
I also started using a volume pedal between guitar and amp, because I found that my single channel amp cleaned up well (much better than any single channel of a channel-switcher) as I backed off the volume.
For the few cases where I want a really intense distortion, I'll use a fuzzbox.
I've reached the point where I'm about to buy one more single-channel amp (my second). I'm seriously considering selling all of my channel switchers... partly because I don't use them as they're intended, partly because the single-channel amps sound better, and partly because I need to replenish my bank account to cover the cost of the new amp.
Anyhow, that's my take on the single-channel vs. channel switcher argument. Obviously, it helps that I'm playing my own material and I get to choose the sound. If you're playing authentic covers, you've got a lot more constraints - a channel switcher (or better, perhaps, a digital amp) is probably going match your needs better.