Having owned various models and barrel lengths of both the S&W L (and N) frame and the Ruger GP-100, the one DA .357 I kept is a four inch GP-100. I think the first six inch one I had shot better, but it got sold a long time ago.
Best advice I can give for anyone is to try both and pick the one that suits you best.
Walkingwolf, Ruger makes a compact grip for the GP-100, it doesn't sound all that much smaller, but sometimes it doesn't take much to make a big difference. This is where I found it http://shopruger.com/Rubber-Grips-wi...uctinfo/70084/
Robert