Hi,
Welcome to the forum!
The best Range Rover is the one that has the most warranty left on it.

Of course I'm joking...
You kind of have to decide what year range looks the best to you. Some people really like the look of the classic while others think the current version is the one they want.
If you are going for a RR that falls in the current body style, you have it made. You can find great deals on the early years that essentially look like the new ones to the untrained eye.
I would say that the most recent years, 08-2010 are the most desirable to me as they have some features the older ones don't have.
As far as the classic and 4.6 years, I think the air suspension is the number one issue on most of them followed by electrical gremlins.
I would visit up the page a little further to the actual Range Rover section to get a decent cross section of what people are dealing with. You can then decide if you want an older version or the newest.
Good luck!
Rob