Guillermo Vilas certainly had one of the finest backhands of all time. The man had a wrist of steel. I saw him hit a ball that landed very short and close to the net and perhaps about two or three feet above the net and Vilas flicked his backhand and hit the ball into the stands behind the court. That was awesome strength. I've seen Laver do similar things with his backhand.
I've always thought that in today's day and age with his excellent speed and heavy topspin power (plus super stamina) that Vilas would be a nightmare today to play against. I think he would be quite similar to Nadal except with a one handed backhand.