I prefer 3 1/2 to 3.7" overall with a blade length of 3" or under. If at work, it needs to be on the smaller side. A Kiwi or Kopa might do there - both very small.
I alter sharpening methods depending on the steel. For modern hard knife stainless steels, I may use a belt sander if a blade needs some work, or Spyderco benchstones. If a touchup is in order, I use a 2-sided strop with 1200 grit Clover Carborundum Compound on one side, and a very fine diamond paste on the other.
If I am dealing with traditional steels, I tend to like my Norton Lilly White Washita, followed by a hard select, translucent or black Arkansas stone and a strop.