For me, Mouser has always executed with near perfection, and I'm very happy to do business with them.
Digikey, on the other hand, has messed up in one way or another on fully half of my recent orders, including my last 3 orders in a row. They usually respond with "we have to do an investigation", almost like they are making a threat, before they will take care of it. Dudes, your repeated failures to pick the right parts, or to have what you say is in stock actually exist in stock, etc., is your problem, don't make it mine! (In fairness, you can actually reach a person when a problem arises pretty easily.)