When i was a kid, it was Brazil, which i still find pretty beautiful. But i would have to say Nepal. Also, even though it's hard to see as a discrete image apart from our experiences, the US flag is pretty f-ing cool-looking.
Antarctica over Nepal by a nose. Nepal's isn't square, which is awesome, but Antarctica's is simply a map of Antartica! What's the point of flags if we all just draw the geographic shape of the country on them? I love it.