For a semi-auto,
I would say the best mass produced rifle would be a M1 Garand/M-14.
For a bolt
Mauser 98 (any rifle that stayed on the front line 50 years and influence every bolt rifle introduced after it must of been a good design)
An AK naaah I think there have been more of these than the Mausers produced but lets face it, they will always sport their average machining from when they were built.