I have tried them both and from my personal experience, I like fiberglass better for most cases. It can be applied more percisly and when you mix the resin exactly per the instructions it is way more predictable as for working times. There is less waste with the glass since it cures slower you have more time to apply it. On the downside you really should only ever use it on the inside of a piece unless you have a million years to sand it down. LOL Hope this helps