The original poster got it right - my favorite is Rocky Mountain High. Man, I love that album. And the song Rocky Mountain High has my favorite acoustic guitar riff ever. That riff apparently came from Mike Taylor, Denver's guitar player at the time. Of course, John Denver's Guilds have been well documented. Based on period live footage (1972-1973) I've seen on YouTube, Mike Taylor was also playing a Guild dreadnought of some kind - hard to say exactly which model because I never saw the back. Definitely had a Chesterfield inlay. It could have been a D-40 or D-50, something like that. It's too bad that Mike Taylor wasn't around after about 1973 or so - Denver definitely made some of his best music with him.
Any of the John Denver records, live recordings, TV appearances, etc up to about 1976 or so have heavy Guild content. I think Denver did as much to popularize Guilds as anybody else at that time.