I've mainly been using Mobil 1 High Mileage or Rotella T6 at Walmart for years now. It always seems to be the cheapest place to get oil.
I posted a thread here recently about brand perception because I've noticed that I'm not basing my bias toward purchasing Mobil 1 on anything scientific. I've seen a lot of good things about Rotella T6 here and on various car forums, so it's always seemed like the best oil for the price. The Mobil 1 HM has always seemed like a good option because my cars all have high mileage and I want to keep the engines clean. I don't know if it's necessarily better for that, though. I have no idea why I've always purchased it over any other high mileage synthetic.
The only conventional oil I've ever used was Castrol GTX, years ago, in my first car. I've had multiple turbo cars, and have only used synthetic because I got used to it.