I like flags that make me go 'huh'
Antartica:

Isle of Man:

Seychelles: (Because everyone goes horizontal or vertical, so let's say screw it! We're going perspective diagonal!)

But favorite... that's a hard one... I always loved the Canadian flag. Because who looks at a leaf and goes 'yes this is a good idea. The maple tree is not all over Canada, only in certain areas. But screw it! This will represent the country.'

But in all seriousness, I do like the Canadian flag. But I'm biased :3