Taking a pole on oil brands
(PLEASE POST WHY IF YOU HAVE A REASON, besides its what I can steal from my hanger mate. 
)
Assuming a normally aspirated Lycoming (I)O-320 or (I)O-360.
Option 1: Phillips X/C 20w-50 ($31 a 12 pak case)
Option 2: Exxon Elite 20w50 at ($50 a 12 pak case)
Option 3: Aeroshell 15w50 at ($55 a 12 pak case)
Option 4: Aeroshell Single grade ($37 a 12 pak case)
Option 5: Other Brand
I personally have great experience with the Phillips X/C and the price ain't bad.
On another list the topic of corrosion resistance (for a plane doing hanger queen duty) is better with the other brands. That may be true, but I think flying regularly is better than any oil. G