OEM or NAPA. They’re the only ones that source OEM quality. Everyone else has lesser grades. Even RockAuto (who is amazing for getting part numbers) has issues with quality from time to time.

Worldpac (no longer owned by AdvanceAuto Parts btw)

If I need it now, I'll go to any major auto parts store. They're all decent imo, so whatever's closest, but if you put a gun to my head and told me to pick I'd probably go O'Reilly's. If I can wait for shipping and I need a few things at once, I'll do rockauto, and for anything harder to find I do eBay, maybe Amazon but they suck so I avoid them if I can. And occasionally I'll go to a third party site if it's the only place I can find something.

I don't have firsthand experience but I've been meaning to swing by the local parts yard to see if I can find hatch mat and other bits and pieces.

Rockauto if I can wait a week otherwise it's the local Autozone/O'Reilly. Rockauto prices are way better and the selection of parts (including quality stuff) is so much better.

My goto is usually rock auto. Other places can be cheaper but nowhere else has everything in on place. If I need something quickly then I just go to my local parts shop.

For most stuff like brake pads, wipers, or bulbs I have used Autozone or O'Reilly, not really picky about either. When I needed the occasional expensive thing like batteries or an alternator I would check prices first and pick the one that was lower for the one I wanted.

This was mostly due to needing the thing right away, so I'm paying a little more for convenience.

I also used LKQ a couple times over a decade ago for junkyard parts like a headlight housing that was damaged.

Haven't had to do the expensive stuff for quite a few years, just wipers and the occasional brake pads.

Varies between Autozone, FCPEuro, Amazon, Ebay and the junkyard. Saved quite a bit with junkyard parts.

Generally toyotapartsdeal.com because their prices are pretty good.

For generic non-OEM stuff I almost always use rockauto

At the carparters.

Depends on the job, special tools and workspace needed, and time.

I recently had a mechanic replace a wheel hub assembly for me. He sourced the parts, finding them for about 5% cheaper than I could find them. His labor rates were very reasonable. And I don't have a lot of time for that sort of job, nor space to do it efficiently where I currently live. Could I have done it? Yes. But he got it done in 3 hours where it would have taken me the better part of the weekend.

Rockauto.com

But parts quality can vary a bit. Still, it's so much cheaper than anywhere else it's worth a little risk.

I'm no mechanic, but I can do brakes. I found the best deal on Rock Auto the last time I did my own.

I usually see if I can get it from Amazon since we already have Prime. Rock Auto is typically cheaper on the actual part price, but the shipping almost always puts it over Amazon's price for me. I use Rock Auto to confirm part numbers though, as it's easier to see a big list of them than the Amazon page giant results mixed in with their "recommendations."

Halfords

If it's an OEM part that I need, I usually use the car manufacturer's parts catalog to find a part number. Then I enter that part number in a web browser, and browse through whatever comes up to find the lowest price from a trustworthy source (usually a car dealer online somewhere that sells/ships parts and has an online store, but sometimes eBay, Amazon, etc.)

Aftermarket parts get a little more complicated because it depends entirely on what kind of part you're looking for.