I can vouch for moo, their cards are of supreme quality. I recently ordered their "Luxe" package (http://instagram.com/p/VSk6m0gg9n/). Everyone I hand my card too is impressed.
Shocked www.4by6.com is not on there. I have always gotten business cards printed through them if I order cards online. Still, some good insight.
If anyone is interested in edge colored cards, Oubly truly delivers. https://www.oubly.com/premium-business-cards
They offer samples kits of the edge color swatches as well.