So I have never ordered to much online as far as auto parts go. I am in need of brakes and rotors for my truck and am considering ordering them in this time, as I can get them much cheaper that way.

Do you guys have a favorite online retailer for this kind of stuff?

Rock Auto

If you use Rockauto, be sure to check the shipping cost. If the items are sent from more than one location, that doubles the shipping cost. I ordered several parts that were on closeout but they came from three locations and that cancelled out the savings from closeout.
If you are Amazon Prime, the shipping is free on most items. Sometimes the prices are a lot less than local. The downside is if parts are wrong, you waste a lot of time. I get lifetime warranty on local parts with more convenient replacement. I drive my vehicles until they drop and the lifetime replacement is good to me.

Yep, considering a possible return is why I shop local. Some parts can be had cheap enough to take the chance, but most are close enough its not.

Summit racing. Big selection with good prices

I found out a little cheat for this. I always used Rock Auto but the shipping always killed me. If you go online to the Advanced Auto, they generally have coupons up to 25% off, if you order online and pick up in store. Has saved me a ton of money, and don't have to worry if I have to return.

Rock auto is the cheapest, just make sure to get name brand stuff. Some sort d their cheap stuff is garbage. And make sure you order the right stuff the first time, because returns are a nightmare. Customer service is zero.

Rock auto ! Just make sure it all ships from the same place .

Go to Rock Auto and list your vehicle with them, then they will send you a list of close out parts that are dirt cheap in the future. Their regular prices are very reasonable generally.

X all above.
Be careful with Amazon auto parts some of their stuff is pure garbage.

Rock Auto on some stuff but I tend to lean towards Napa locally if I think I need to return or replace during warranty period

I've used Rock Auto and Parts Geek. For brake pads and rotors I've been using Ebay, usually find them cheaper and free shipping.

Rock auto here, too. Great service, fast shipping.

I buy most everything through amazon or ebay motors, never a problem and cheaper than Rock Auto most of the time. Watch the reviews and only deal with the bigger suppliers.

Check those prices on line and local I needed a quart of brake fluid looked at Amazon it was $11+, the same bottle local was $5+ so free shipping might not be free.