Preferably hard and/or military sci-fi, not part of a series, with an audiobook available. Humor is a bonus, but not necessary.
I read only Starship Troopers when it comes to Heinlein, so I suspect I'll end up with one of his books, but I'm open to suggestions.
I'm also considering picking something using this flowchart.
I'll only add that I listened to Scalzi's Old Man's War series and Redshirts, and enjoyed them.