Most of the larger divided highways around here have good wide shoulders on them. I like them because their grades are even. Not like a hill around here that I call "The hill of never ending perpetual sorrow" as it changes grades several times over a half mile. With an even grade, I can get into a zone where heart rate, speed and cadence all come together.
I also spend a lot of time on winding 2 lane roads. I pay attention to cars approaching from behind and try to work with them so that I interfere as little as possible. Since most of my riding is during commute times, these are often the same people that I see regularly.