Such a question is always likely to spark brand loyalty wars here

, but I'll brave it! At my 4,000 interval, I changed to the synthetic Amsoil fluid. I have had good luck with it in my Ford 8.8, and decided to try the Wing. Some 10,000 miles later all is still well. It didn't increase gas mileage anything noticable, didn't make all days sunny, and didn't help me win the lottery - but it seems to be lubing my final drive just fine. Which is all I expected! I believe that any brand will do the job when changed regularly and do think that most syns are better than dino. Mobil 1, Castrol, and others make good syn lube. My choice was based on past experience, availability, and cost.
Good luck,
Chris