If you want to know more about oil than anyone needs to, go hang out over at Bobistheoilguy.com.
One of the VW TDI forums has a ton of info on diesel specific oils for the VWs.
Were it mine, and I wanted to save money, Id run Shell Rotella T 5W40 and call it a day. Nothing better for its price, assuming you arent paying the same as every other oil like lots of auto parts stores like to do.
Best of the best? Mobil Delvac 1 5w40.
Best of the rest? Mobil 1 TDT 5w40. Easier to find and not quite as expensive as the Delvac 1.
I dont run non synthetic in anything. Not much reason to unless you want to save a few dollars per gallon.
My engines just about all get 5w40 TDT. Thats push mowers, the 20hp Onan in my 318, the 23hp Kawasaki on the Exmark, and now the 2025R.
I did a massive amount of reading on oil analysis, wear patterns, etc with lots of different oils, and what a couple different forums conclusions were based on a lot more data than I ever want to see, and that conclusion was that for my money, TDT is it, hands down.
Every once in a while, Delvac 1 has a rebate. I buy about 4 gallons of that when it happens. My TDI has 10,000 mile intervals, so it lasts a while. Currently, that car has 333,xxx miles on it, and I plan to teach my 3 year old to drive it.
Before I actively looked for rebates to get the better oil, because why pay full price if you dont have to, I ran Rotella T 5w40 in quite a bit of stuff, including my motorcycles. It is truly a great oil, and very hard to beat. Why switch? Because its not recommended for the TDI, and since I was buying it at a discount anyway, the TDT was the same or less money.