I use 10" for houses and 12" for commercial.
For some commercial work where there is a lot of repeated windows, we cut channels to size. Some are bigger, some smaller.
I also always have a 6" channel in my pocket. It's suprising how many times I use it.
As for the mop, I use 2 sizes, 16" and 10". It's incredible how much time can be saved with a larger mop especially with commercial work and large paines of glass when using a pole.
Also, I dog ear every channel just to the amount I like.