I believe there is no MAIN factor to consider when ranking the greats after Slam Wins.
It's a question that I thought about for a long time... but now I've developed my own method towards comparing all-time greats. Maybe it has its flaws, but I believe it's the best way to do it.
#1 Comes the number of Slam wins. Since I believe it's unfair that Player A with 2 Slams and an "average" career could be ranked below a Player B who might've won only 1 slam but was a top ten player for a long time, reached many Slam finals, etc., I determined that having a 2-slam difference was enough for one player to be above the other. Therefore, if Player A won 6 slams and Player B "only" 5, then A is not better than B, it deserves a further analysis.
#2 Comes a most-detailed analysis, because there is no consensus in the tennis world that "Weeks at No.1", "Years in Top Ten", or "Slam finals" is the second factor to take into account when analysing GOAT-ness.
You might wonder what this analysis is?
Here's a snapshot of an Excel graph I did with it when comparing Mauresmo with Azarenka...
I think it is a just system, for example, when analysing 3 & 4 Slam winners I got:
Maria Sharapova (might need some updating now, after such a great 2012)
What do you think of it?