I agree with what LinacMan says about thinner materials vs stiffer materials. I do think silk bowties are easier to tie than cotton.
I think if you're looking at a shirt that you wouldn't wear a necktie with, you probably wouldn't wear a bowtie with it, either (the exceptions being the pleated shirt worn with a tuxedo or the marcella dress shirt worn with tails). Similarly, a pattern that looks ugly to you as a necktie isn't likely to make a great-looking bowtie. But that's a matter of personal taste.