Something to consider when buying tires is not just the price per tire, but the costs of installation, and how they are installed. Places like Sam's club and Costco might have lower tire prices that are even better after the $70 Michelin rebate, but so what if they don't do such a great job installing and balancing them, or what if they damage the wheels in the process?
I had nothing but positive experiences with Discount Tire. Stellar service, they gave me no hassle of any kind about the size of the tires, how I wanted them installed, or any of that.
I no longer have a Discount Tire nearby and am stuck buying Michelins at Sam's. They refuse to buy new tire machines even though the old ones are broken and missing the pads for use with alloy wheels. Consequently, every set of tires they install on alloy wheels results in the alloy wheels being damaged by the gripper teeth made for steel wheels. I now have eight big gouges on each wheel of the Explorer, not to mention gouges on what were brand new alloy wheels of some other brand new vehicles.
Hopefully it's not the case, but my guess is there are plenty of Costco's that operate similarly. About all you can do is speak with the shop manager and ask to see how they install tires and inspect the equipment. I would strongly consider Discount Tire though, even if their per-tire price is higher, you should still be able to get the $70 rebate, and the higher level of service is worth more in my book.