Th Doug may be more boring than many of the others, but it's solid. The flag from the Republic of Cascadia's website is just too... squiggly. The waves draw the eye off the top and bottom of the flag, making the entire thing seem unfocused.
If you really want to have more action on your flag, these two do it tastefully:
Flag of the Cascadian National Party
Flag of the Cascadian Institute
Here's , if other people want to have a stake in the conversation.
FWIW Sara is extremely classy and has a wonderful eye for aesthetics.