2018 Volvo VNL 780, 16K miles. Decided to change oil. What oil best?

That's another plan.
Are you buying it out right? What's the expected residual value on your truck at 500,000 miles?

 

What do you expect to sell it for when it is at 500k?

 

Synthetic has everything to do with longer oil life. This is why people use it. It doesn't break down, but will get dirty. As others have mentioned, keeping It clean really helps. Magnetic drain plug is good too.

 

I'm assuming this has a d13? If so you have a factory bypass filtration system. That extends your drains way out. Check your manual. I changed mine at 50-60k kms, 30+k miles and sampled EVERY change and the samples looked supreme. Volvo calls for 10w30 I used synthetic in the winter to aid in cold starts. NEVER idled the truck and it started down to -20 no sweat. The volvo are made for cold weather. I used Rotella in the warm months. 15-40. Same drain intervals. I had a hard time leaving the oil go so long and did my first change at 15k miles but a friend said to let it go. I never went to distance, couldn't do it. He does regularly and his samples are pristine. I didn't idle my truck much at all and my dpf cleaning at 730k kms was not even needed. Filter barely contained anything. Mechanics chalked it up to no idling. That is a good motor treat it well it will treat you well.