I've used both sites, and the fees on Vivid are a little higher, but they start ticket prices a little lower for the same seats (some scalpers list on both). So in some cases, I've saved a few bucks using Vivid for the same seat, compared to StubHub. I usually check both places.
I agree that StubHub is a better experience, plus they offer rewards and birthday coupons. They are my preferred site, usually.