The 55-300 will have optics that aren't quite as good as the 70-300. It's also a less complex lens design, if I remember right. As far as used vs refurbished, both have good deals that can be had. I took a look at the link from Amazon, and honestly, it's worth the risk, provided the seller has a good rating and AMOUNT of ratings. Just because one or two people have a good experience, doesn't mean that everyone will. I tend to look at the sellers who have both high ratings and a lot of people (50 or more) saying they're good to deal with.