A short summary that is not intended to claim anything about the quality of different brand oils.

AMSoil - Group 4 Synthetic (Not API certified)
AMSoil - Group 3 Synthetic XL7500 Series (API certified)

Mobil1 - Group 4 Synthetic (API certified) - now offering a product for 15,000 miles

Royal Purple - Group 4 Synthetic (API certified)

Redline - Group 5 (unknown in API cerfitied) - Poyol Ester Base Stocks vs. PAO (Group 4), Tri-Synthetic synthetic contains PEs as well.

Castrol - Group 3 Synthetic(API certified)

Pennzoil - Group 3 Synthetic (API certified)

Valvoline - Group 3 Synthetic (API certified)

In my opinion, all the the Group 4 synthetics are fairly equivalent...I personally don't know enough to be convinced in any one direction.  I find it interesting that AMSoil compares to Mobil 1 on their website but not Redline or Royal Purple, also strange that they are not API certified (I wouldn't use it in a vehicle still under warranty).  For me Mobil 1 is the easiest to get locally, so it is my choice for my Tundra.  I am thinking Valvoline or Mobil 1 high mileage for the 85, synthetic doesn't stay within the boudaries of my motor when I tried the Castrol Syntec (Group 3) is became a fountain.