At the moment I'm using Mobil 15w 50 fully synthetic.
Not sure if its regarded as a "brand name" like millers etc, but At the moment i can get 5L for about £40, so its good value for me.
I'm not convinced that returning catch can to sump is a great idea.
I often find the oil has gone quite like sludge due to the condensation that gathers in the can on cold starts. Then this mixes with the oil and makes for a really horrible combination!
However having emptied it before going on track, and emptying it just after, the oil that came out was perfect.