Variety = good. Some hit the wrong shot at the wrong time but in general, variety = good.
Also, I feel like you need variety to handle different situation.
Opponent has mediocre serve, OK you only need a compact topspin style return.
Opponent has really, really big serve, you need a block slice return. I will use an underspin block on the FH and BH if the serve is huge. Nalbandian and Federer do this.
Low ball in mid-court area, you need to the ability to slice it back deep.
Normal rally ball, hit normal topspin strokes.
Super wide hard ball while at baseline, you need squash style slice on FH and BH sides.
You need variety to be a complete player.