I feel more comfortable ranking Open Era players. I'm going to include the entire records of Laver and Rosewall, because they remained great into the Open Era era, yet their Open Era records don't reflect their overall greatness (contrary to Pancho, who was similarly great, but in the 50s and still very good in the early years of the Open Era, but not really an Open Era great).
10 Greatest Players of the Open Era
1. Laver
2. Federer
3. Rosewall
4. Nadal
5. Sampras
6. Djokovic
7. Lendl
8. Borg
9. McEnroe
10. Connors
I'd be happy ranking Lendl, Borg, and Mac in any order, but ahead of Connors and below Novak.
Agassi would be next, then a drop to Newcombe, Becker, Edberg, Wilander, Murray, Vilas, Nastase, Ashe, and Courier to round out the top 20.
If Roger wins a couple more Slams, he passes Laver. They're already a close 1-2, but Laver's overall record and dominance is still greater. That said, I might be over-compensating because Roger's my favorite.
Nadal may deserve to be ahead of Rosewall, but his record is marred by inconsistency as it shows up in his relative low weeks at #1. But if he wins another Slam this year and is YE1, I'd push him past Muscles. Novak also has a chance of surpassing Pete and Rosewall, but needs to bounce back in a big way.
If I were to add Gonzales to this list, he'd be between Federer and Rosewall.