The obvious answer would be a swing that gets a hole in one - but this is far too generalised and it is sometimes impossible to get a hole I none from teeing off due to the shape of a golf course and the position of the green in relation to the fairway.
Instead it is better to think of what contributes to a good golf swing so that you can ensure your swing is as good as it can be, and these are things such as - Excellent posture of the golfer - this is essential to a good swing as the posture of the golfer creates the foundations of the swing.
The speed of the swing - any good golfer will tell you that one of the biggest mistakes you can make is to think that by swinging the club as fast as you can will create a great deal of force which will make the ball travel further.
Trying to do this usually results in a poor swing which often sends the ball in the left hand direction rather than straight ahead.
Concentration - when you are lining up your shot before the swing you should make sure that you have your eyes on the ball and are calm yet fixed on the task in hand.
Loss of concentration is a killer if you want to have a good golf swing.
Co-ordination - good co-ordination comes from practising your swing time and time again.
Without this you will not naturally swing the club and the movement will feel forced and will not help you to perform well at all.
If you want to succeed in golf practise makes perfect so spend as much time on your swing as you can to get it right.