Bar length depends a lot on how tall you are, me personally, I only ever run 25 inch bars on about every saw I have, saves bending over so much to cut stuff up it seems, also helps give that little added reach a person wants.
Having a balanced saw is ideal, but to run one all day long, if a longer bar and being unbalanced saves bending over, I'll take the longer bar every time, at the end of the day, my back doesn't hurt so much.
I also run a 36 inch bar on the large saw if we're felling large diameter tree's, but its not too often its needed, we also have 16 and 20 inch bars and being the pro line of stihl saws, all bars are interchangeable, same goes for rim drivers.
We also mix and match 3/8's and 404 chain, bar and drivers as well depending on what we're doing, so the bar selection is quite large on hand.