Sideburns, Mustaches, and Muttonchops.
To get a 1700s/1800s feel for my imperial minifigs, I like heads w/ sideburns, bushy mustaches, and muttonchops. Stubble is fine, but I'd rather they looked sharp. The soul patch head is goofy but acceptable. I like to save beards for my pirates.
Are there other heads out there that you know of that I should take a look at? Given the choice, I like the ones with the white eye pupils.