Polar pattern is really beautiful. I always enjoy looking at it. It's simple but so... captiving, mesmerizing... Plus, it's my regional pattern, too, so I was really happy about that.
Apart of that one, I truly like Fancy pattern, River pattern, Sun pattern and Monsoon pattern.
I'm actually rather partial to the Vivillon in my region, the High Plains pattern. ^_^ I just really like the strong rectangle/square sort of shapes in it. But, I also really love the bright yellow Continental Vivillon as well!