A K&N filter is going to allow more air flow but at the same time they will allow larger particles through into the carb. If you are riding in ideal contions like a prepped track, K&N is great. If you ride in dusty/muddy/wet/ect... I would choose the UNI. I personally prefer a foam filter. I run UNI and NoToil. A foam filter with an open airbox is just as goos as a K&N.