I have the pull-over type. My horse is perfectly fine with it and it provides a relatively seamless look and feel and I don't have worry about catching any long hairs or whiskers in the zipper during the winter. My best friend has a zipper and a pull-over and the zipper one has pulled out a lot of hair over the years - albeit unintentionally. For me, the pull-over hasn't messed up my horse's mane or braids at all. His mane always looks just as nice as a horse's mane with a zipper sleazy. I like them both and find that I tend to leave the zipper-type zipped and just slide them on and off anyway.
The wind of heaven is that which blows between a horse's ears. ~Arabian Proverb