Yes, I sometimes posted that, in my humble opinion, 4 slots of time stand up.
The middle to late 50´s ( and I will mix up pros and maateurs because we talk about the global situation of the sport) were great: Laver reached major finals in 1959, Olmedo was superb, Emerson and Fraser, as well as Cooper and Anderson started to stablish themselves as top stuff and, of course, kramer,Trabert,Hoad,Rosewall,Gonzales and Sedgman is probably the best group of six players assembled at the same time.
early 70´s were just as great, I consider the first great open era starting in 1968 and ending around 1974, when the game changed a lot.During those 5-6 years, Laver,Rosewall,Nastase,Ashe,Newk,Gimeno,Kodes,Roche,Smith and Okker ( with still competitive Emmo,Stolle,Drysdale,ralston,Lutz,Richey,Gorman,Pilic,franulovic,Metrevali,taylor,Gorman right behind) will make what is, in my opinion, the greatest ever top ten.Better than late 50´s because the deepth was a bit better at the top 10 or top 15 ( which is what defines true competitive eras)
Of course, the whole 80´s were a feast with Borg,Connors,Lendl,Mac and later Wilander,Becker,edberg ( and Kriek,Cash,Noah,Gomez,Mecir and for a while Vilas;Gerulaitis,Tanner,Pecci,Mayer and Clerc) going at each other.if Borg had played until 29 or 30, I just can imagine a 1985 year with Bjorn,Jimmy,John,Ivan,Matts,Boris and Stefan that would have been unbelievable and with a far stronger media and financial support than the group of the late 50´s and even early 70´s.
Finally, the first 5-6 years of the 90´s were also huge, with Sampras,Agassi,becker,Edberg,Ivanisevic,Bruguera,Rafter,Courier,Chang,Stich and Richard Krajicek well supported by guys like Kafelnikov,young Moya and young Rios,Korda,Rusedski,Muster,Forget,Medvedev,Todd Martin and wayne Ferreira among some others.This group compares to any other formed.
So, the top 6 is late 50´s, the top 7 is the 80´s, the top 10 is early 70´s and early 90´s.Sorry for the long explanation, but it is the way I always will look at this sport unless things will change in the next decades.