I prefer Jenson USA because the website interface is so much better. I can't stand Nashbar's "More Results" links. Performance's listings are more picture than info. Supergo's is really nice, but I have yet to order from there (I have however used all the others.)
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Now onto all those things you said are the same:
Nashbar used USPS for standard shipping and it took 9 days to get from Ohio to Georgia. Jenson and Performance used FedEx ground or supersaver. Shipping from Jenson in CA to GA took 7 days, but at least I had a tracking number to see where it was. To make my Nashbar purchase worse, they used the thinnest cardboard box I've ever seen. They put in two sheets of cardboard paper that did about nothing. My shift lever box was burst open and there was a dent in my book (yeah maybe a little picky).
I also like having a login to check order status at Jenson. I can check it at work, without having to remember my order number (like Nashbar/Performance). They're order status also shows when the expect backordered items to arrive. Nashbar's doesn't even show the price.
Nashbar's advantage is having a little bit lower end stuff for really cheap. Jenson would price match, but they don't carry some of the stuff that Nashbar manages to sell for rock bottom. I'm about to try Nashbar again and pay the extra 3 bucks for 2 day FedEx.