I just sold my '02 Q and bought an off-lease '04 Phaeton. The Bentley Continental Flying Spur is considered a true REBADGED Phaeton.
Go with the V8, which is similar to the Audi A8 engine, and you will have less risk than you would with regards to repairs on the W12. It's a great engine.
Also, most of these off lease Phaetons (there were only about 3,000 total sold in NAR between 04-06) will come with VW CPO warranty.
Fit and finish of the Phaeton is amazing. Also it's got a lot of interior room, which I needed compared to the Q. That coupled with the climate system, air suspension, 6 speed transmission, massage seats, etc. make the car truly amazing.
I liked the Q, I love the Phaeton. Either choice puts you in with a group of owners who enjoy quirky cars.
VW service ain't too bad, and there are several VW dealers that are Bentley dealer as well that may have better trained technicians to work on the Phaeton since it is so similar to the Flying Spur/Continental GT.
There is a great Phaeton forum at
http://www.vwvortex.com.
Good Luck!!