I believe that there have been three great competitive era’s in men’s tennis over the last fifty years or so. Certainly the current generation of players including Federer, Nadal, and Djokovic along with perhaps Murray and Wawrinka at times would be one.
The 1990s was an exceptional era that included the likes of Sampras, Aggasi, Becker, Courier, Edberg, and Chang. Certainly a formidable collection of greats.
And perhaps my favorite era, at least to watch, would be Connors, McEnroe, and Borg along with a few years later Wilander and then Lendl although he was really mid to late 1980s.
Tough call. The 1990s really was a great time for tennis. As the years go by sometimes we tend to overlook or forget just how good the level of competition was. I think the number of players capable of winning a Grand Slam title was probably never better than the 1990s. Today it’s a pretty safe bet that it will be one of the current big three.