I think it all depends how you like to ride! Some people like the rear tire to break loose 1st and believe the 2.6” tire is more precise as there is less flex when compare to the 2.8. Better for turning.
The 2.8” tire will be more compliant over bumps/rocks and hook up well, including turns.
I personally prefer the 2.8 tires, but had problems keeping air in them. I went threw like 5 2.8” tires all suffering cut tire casings. So I now use 2.5-2.6 tires in the rear.
2.8 Michelin E Ride or Maxxis DHR have sturdy sidewalls with no/little flex and have more traction then the 2.6 variant. I felt the 2.6 was lacking when breaking.