I run Amsoil in the crankcase. I have no complaints. For reference, Amsoil makes a couple of different full synthetics. They have one that is pretty much the same as any other synthetic, then they have one that they rate for 25,000 miles. The regular one is cheaper, the 25,000 one is around $6 to $7 a quart. I run the extended stuff just because I put a lot of highway miles on my car and don't have the time to change it every 3,000 miles. Right now I'm changing it every 9,000 or so.
I must say, when I switched from Mobil 1 to Amsoil, it seemed like I got higher oil pressure, but then again this could just be the placebo effect kicking in.
'96 Jade SLE "Twilight" -- Sold :(
'01 Silver Grand Prix SE
'88 SBC Ford Mustang Convertible (work in progress)
'72 Mustang Hardtop
'06 MINI Cooper *