Its difficult to pin down what the "best" rifle is as there are too many variables: weight, ergonomics, accuracy, reliability, capacity, cartridge capabilities, etc etc etc ad nauseum. When built by a quality company: the AK47/AKM (in 5.45, 5.56, 7.62x39), AR15 (in 5.56), and FAL (7.62x51) are all the best at one or more of the criteria mentioned above.
At the end of the day, reliability is my first priority.