I don't even want to think about how much money I've spent at Summit, it's probably close to tens of thousands. Darn near everything I order comes from there. Spark plugs, oil, my Hotchkis and Hellwig sway bars, my QA1 LCA's, the holley 750 ultra DP on my Duster, intake manifolds, exhaust systems, paint and body work supplies, sheetmetal, engine internals, the wheels on my Challenger, heck even the T56 Magnum transmission for my T56 swap. I've bought from them for well over a decade now.
I think in all of that time and probably hundreds of orders I've had to send one or two things back? And the one time they sent me the wrong part by accident the right one was on my doorstep the day after I called them. They're one of the best in the business as far as I'm concerned, hands down. I almost always get everything I order the next day if it comes out of Sparks, and when part of an order comes from further away I find that they'll often upgrade the shipping on that part. Not because I rushed the order or paid for more shipping, but to have everything arrive at the same time. I know some of my experience is based on being a couple hours from the Sparks warehouse, but their customer service has been amazing the couple of times I've had to use it too.
The only other places I usually get parts from are the smaller specialty companies like DoctorDiff, Bergman AutoCraft, FirmFeel, Hughes, etc. I've mostly stopped using RockAuto just because by the time you pay shipping and wait a week or two for the stuff to show up any savings has evaporated. Jegs takes forever to get stuff to me, although that's not really the companies fault, just a warehouse location problem. But I rarely buy from them either, Summit is by far the best to deal with IMHO.