Castrol synthetic or Valvoline?

After running the 5.9 Magnum for 9 months and finding it uses ZERO oil after 10,000 or so miles I am going to change to a full synthetic oil.
Thinking to go with a 10-30 full synthetic in the Castrol or Valvoline line.
I have run and trusted both brands for decades and was wondering if anyone has a preference between the two in synthetic form and why.

Also, I am a little apprehensive about going thinner like 5-30 or 0-30.
Would there be any good reason for oil that thin other than better heat transfer?

Switching from Castrol Dino 10-40 and I use the black Napa Wix/Mopar filters.

Thanks