I used Mobil 1 when it first came out. It was more expensive, and I didn't notice any difference.
Castrol Edge is marked full synthetic, but if you're under about 40, you're probably not aware of the Mobil1 vs. Castrol feud. AFAIK, there is no such thing as 100% synthetic oi, because they need some fossil oil for the additives to stay in suspension. Also, unless it's changed Castrol is only about 50% synthetic. It's all I use, since many VW dealers use it, and it's readily available at Advance Auto Supply. I keep a quart at home to top off when I'm a half-quart low. I change about every 4,000 miles and believe in keeping the sump full. More oil equals better cooling. I have under 32,000 miles on my 8-1/2-year-old R so I could probably use anything that meets VW specs, but like the OP mentioned, some people are just loyal to oil, just like they're loyal to some car brands or tires. I only buy Michelin PS4S' for their superior wet traction. They certainly don't last very long.