I have a 2007 EIGER. I used to run the Valvoline atv 10w40 oil but I switched to Rotella T6 5w40. I think the T6 warms up a little faster. so far no problems with it Its been i since October and I use the quad alot

 

I use both. I run the Mobil 10-W-40 4T in my Raptor. I use a synthetic in that because I only change the quads oil once a year, since I have not been riding it a lot the past two years. I run the Valvoline 10-W-40 Motorcycle oil in my R1 and I have had pretty good luck with it. That's what it has had since day one (with the exception of using Yamalube 2 times) and I have about 24,000 miles on the stock clutch in my bike.

Personally, I like the Valvoline more. Better price, and I think it's a better oil. Lots of people will be quick to bash me on this one for liking the $4/quart oil over the $10+/quart oil but plain and simple I think it is better stuff! Just because something costs more money does not make it better.

Generally speaking, they are both good oils, both Mobil and Valvoline make good products and do lots of testing!