I was on my way to Central America and over heard a military call sign checking in with CENAMER Control, checked in at Angels 600 or something and sounded like he was forcing his voice through an oxygen mask? This was on VHF.
Angels is used mainly by Navy guys, wonder where that guy started out.
As for the UHF/VHF, anytime I go cross country I usually use VHF freq's. Two reasons. One, it gives me something to listen too and break up the boredom, and two, it can be a good SA builder. Especially in the terminal area.