May Birthdays 
For playing live, nothing beats a 3 piece for me. It creates the oportunity to musically fly off in different directions without being harmonically fenced in (not that we play too outside, but it's nice to be able to go there). A lot of our on stage cues are basicaly hand or head signals (hand to the ear is "listen cause were going somewhere else", the dynamics hand thing, open or extended sections, use your ears cause I'm gonna break into a tune we've never rehearsed, etc). Playing with the right rhythm section certainly opens things up a lot for me. There's also plenty of room for space too.
Recording-wise it's basically whatever the song calls for (extra guitars, hand claps, keys, steel gtr, sitar). We've gone the heavy overdub route, and I usually dropped some of the parts out in the final mix. Generally I find our songs breathe better with fewer instruments. Sometimes the budget will dictate playing live off the floor with no overdubs. When we are working in our own studio, budget is obviously not a problem.
Listening-wise, I seem to lean more towards 4 piece bands.
So for me, I guess the ideal changes depending on the context. Great thread!
Rev
—Canadian Surf
