What I've learned:
I want bars that are parallel to the direction of travel not perpendicular.
I like my hand position to be low but not racing drop bar low.
I like a fairly wide handle bar for commuting.
This means I like wide drop bars on riser stems or moustache bars. Flat or riser bars are uncomfortable.
I prefer to be fairly stretched out on my bike so I tend to go up a size. If I can stand over the top tube its not too big.
Brooks saddles and fat tires make the ride much more comfortable.
Double wrapping the handle bars with padded tape makes the bars too thick even for my large hands.

Craig