It depends on what you're looking for. People criticize ECS but they are reasonable for quite a few things. Shopdap is good for DSG maintenance. I've ordered from some dealer sites for certain things. Ebay is good for random specific parts if you get oem.
Typically I search for part numbers on Google to shop because it frequently reveals new sources for good prices. Of course there’s the well known sources like Deutche, Pelican, ECS, etc. but occasionally a dealership parts department will pop up that’s worth a look. For example, a few months ago I did a lot of suspension work and needed a lot of fresh hardware to bolt everything back together and a Volkswagen dealsership in Marietta, Georgia (Atlanta suburb) offered the best prices with shipping taken into account.
For non specific parts vendors I also really like PartsGeek. They frequently sell OEM parts along with premium and economy brands.
I messaged you directly but I’d also add that I usually just buy through local dealerships that are willing to sell at their cost or through my local shop - I’m paying local sales tax but if I ever need help dealing with a company or finding a part of any installation I have another person to talk to instead of just trying to deal with an internet company. I like dealing with shops and real people. [emoji106]