One of the major changes of the game has been the different types of shots used. Thirty years ago slice or backspin was the primary shot in tennis (besides hitting the ball flat). A slice ground stroke causes the ball to rotate backwards towards the person who hit the ball. The ball often stays low to the ground after it bounces. Slice shots can be good for making an opponent really stretch for a ball, but it is difficult to hit them with much pace.
Modern tennis is dominated by the use of topspin shots. A ball with topspin rotates forward toward the opponent as it travels through the air. This allow for players to hit with much more pace while still keeping the ball in. Because of the rotation of the ball, players can also hit the ball over the net higher and expect it to still go in.
An experienced tennis player would integrate both types of shots into play using each shot strategically throughout points.
But, if I had to choose just one shot to use, I would pick topspin. I have been raised in the topspin era and love to see the ball sail three feet over the net and drop in at the baseline.
Check out these videos of slice and topspin: