To the OP: In 2009 Borg declare Roger is the greatest tennis player of all time. If you knew it all along, you wouldn't create this thread. Don't feel too bad since you are new to tennis.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi