Both good outfits, usually same prices, though I've found that Summit's shipping is the faster of the two.
I still like catalogs, and Summit's is way better than Jeg's; websites are the same story to a lesser degree for me.
Last Jeg's order included valve stems, which were pictured as a pair so I bought 2; each turned out to be set of 4, so now I have 8. But they were inexpensive, so no worries, and I can think of worse problems to have...