Back in my restoration days I dealt a lot with Year One. I closed shop almost a decade ago, so there was wasn't anywhere near the competition. Maybe National Parts Depot on a national scale and that was primarily it, dealing with a lot of cars across the board. Auto Body Specialties was another I dealt with a lot. Maybe a few others.
I was in the game to get cars done, done well, and make a profit. I was a "commercial" customer for Year One, meaning I didn't pay catalog price to begin with, but could charge catalog price, which was important.
But for me it was all about customer service.
I ordered a top for a '66 LeSabre convertible from Year One. Here's the trick, though: I needed a plastic curtain. LeSabre's came with a glass curtain, but the mechanism to keep the glass flat was missing from the car and the owner didn't want to hunt it down. Year One sent me a top for a Skylark. Got it out of the box and the top was half the size I needed. Called 'em up and explained that wasn't what I needed. Customer service rep took down all the information I could give him and called me back in a couple of hours.
UPS was at my door a day later with a return label to take the Skylark top back and three days later the proper top was in my hand, with a plastic curtain, drop shipped from Legendary. At the same price as the Skylark top.
Yup, the customer rep called Legendary for me, saving me time on the phone, and handled the matter completely professionally.
Things may have changed in the past decade or so, but I was well pleased with Year One.