I'll share my thoughts and try to explain to them...
I use RP 5-20 or Amsoil into my Elantra. RP during summer, Amsoil the rest. I also use either Amsoil or RP oil filter because I think they are the best and my math is:
60$ for oil replacement.
180$ for a year.
1800$ for 10 years. For providing what I think is best oil and best filter for my car. Still beats the price of replacing engine...
And here is why I am using RP and Amsoil. I do think they are the best. Pure and simple. RP has more cleaning agents, worse cold flow, that's why it is in my car during summer. I am using this in my 2 year old Elantra, and was using that system on last 3 years out of my old Nissan Versa.
And I did try couple of other "high end" motor oils, including Pennzoil Ultra, Valvoline, etc. With RP and Amsoil my engine sounds quieter (always good with moving parts in my book) and I usually do get couple more MPG on average.
And here is one thing that happened to me recently... I take my car to dealership because I have Hyndai care inlcuded, which means 3 years of free oil change. I see on the receipt that oil costs about 2$ per QT, I can't even imagine what oil they are putting in. Within 7-10 days I go to my friends house, drain oil, replace oil filter and put AO or RP...
In November, had to go to business trip next day after shop visit and didn't had time to do my oil change... Trip got complicated and I ended up driving about 600 miles in 12 hours or so. I can't even explain difference how engine worked and sound of it at the beginning of the trip and at the end. I actually stopped couple of times to check my oil level because I was sure I was low or something.
At the dealership they always put 3000m on the sticker for next visit, I assumed it was just a way for them to charge more, and that even cheap conventional oil should be good for more than 3K miles...
Long story short, still on the business trip, I went to one of the stores that sell part and do maintenance work and got RP oil and filter in my car. I would prefer amsoil since cold weather was on its way, but RP was the best I could buy at that time.
I could definitely tell that engine was working smoother and quieter, and still is, 3 months and about 1900 miles later.
One thing I've read so many times in this forum is people saying it's not the brand of oil, it's how often you replace it, etc. which I agree, that's why I usually do it every 4 months or about 5K miles whatever comes first. But also it is very important what oil you put in your car.