This stamp is a classic:
Round, because even your dimmest employees will recognise that it’s for international mail. And doesn’t need an airmail sticker.
Undenominated, because it costs what it costs.
Unless, of course, you think it’s worthwhile to stockpile stamps in case the Post Office will keep increases lower than inflation.
Thinks: If the USPS is so smart, how come they’re almost bankrupt…?