Tirerack is what made me a believer in buying tires online. The product / size selection was incredible, this is back in the early-mid 2000's when I'd started ordering from them. When you went to a local tire store, you were limited to what was on the shelf (in your size) or whatever the salesman wanted to sell you. Tirerack always had lower prices than any local store I could find.
Somewhere around 2010-2012ish I discovered Discount Tire Direct, and for a time, they almost always had better prices because they had free shipping. So I'd ordered a couple sets from them. Later on, Tirerack introduced free shipping, so it was a direct comparison instead of doing the math, and I found the prices comparable-- sometimes DTD was cheaper, other times Tirerack. If the prices were the same, I'd always use Tirerack since they included a road hazard guarantee, and I believe in supporting the "little guy."
In the last decade or so I've noticed DTD has a TON of east-asian off-brands, though they do carry a decent selection of what I consider "normal tires". While Tirerack does sell some lesser known import tires, they've always had a better selection of the tires I'd be willing to buy.
With the merger, I hope they don't fill their site with DTD-exclusive tires-- those brands owned by Discount Tires (Arizonian comes to mind) but made in east asian or domestic factories to a price point. I've always considered Discount Tire as the Walmart of tires-- they sell some good brands, but most of what they sell is discount stuff to an audience that knows nothing about tires and don't care about quality or what name is on them.