The Ruger is a bigger heavier gun,designed well after the model 29, and avoiding some of problems the .44 mag can cause.
The 29s have great sights and great triggers, The Rugers are good, but not quite as good in this as the S&W.
The heavier weight and larger (longer) cylinder let the Ruger handle the heavier loads better, including some obscenely heavy bullets too long to fit in the S&W cylinder.
Either one will do well with standard magnum loads, if you want to go to the outer limits, the Ruger will do a bit better than the S&W. More than anyting else, the fit and feel in your hand is the most important thing.
All else being equal (and it almost never is) bigger bullets tend to work better.