I use Shoprunner where it's supported, because I get it for free with Amex. My experience is that it's not as good as Prime. Prime is supposed to give you free delivery in 2 days. Shoprunner is supposed to give you free 2-day shipping. These are very different things. Yes, the Shoprunner package is shipped via a 2-day shipping method, but the merchant often takes several days before they ship it. I've had Shoprunner orders take a week or more to arrive. Every once in a while Prime misses its promise date, but it's pretty rare, and usually only by a day. I don't think I've EVER had a Shoprunner order arrive in 2 days. Unless the merchants are all prepared to start passing orders off to the carriers more quickly, a carrier program will have a hard time matching the Prime experience.
This is pretty typical for most not-amazon (or amazon-competitor) stores, I've found. It's why I am so reluctant to use third party sites, even though I know it's for the better if I do.
Newegg I've found to fulfill the Shoprunner "two day" shipping promise pretty reliably. I actually get a lot of stuff the next day due to being relatively close to their Indiana drop-ship partner/warehouse/whatever.
