Rosewall > Laver
In the Open Era :
Rosewall has 4 Grand Slams
Laver has 5 (including the calendar year Grand Slam)
Pro Slams :
Rosewall has 15
Laver has 8
So Rosewall has 19 Majors compared to Laver's 13.
It's obvious Rosewall is far more successful. And these are some ways in which he is statistically better :
Dominance - Rosewall won 9 consecutive Pro Slams that he participated in. Laver only ever managed 4 Pro Slams in a row and 4 Open Era Grand Slams in a row. His 4 in a row against amateurs isn't comparable.
Longevity - Rosewall won his first Major in 1957 and his last Major in 1972. That's 15 years apart. Laver won his first in 1964 and his last in 1969. Just 5 years apart.
Versatility - Rosewall has 5 Grasscourt Majors, 5 Claycourt Majors, 5 Indoorcourt Majors, 4 Woodcourt Majors. That's 5-5-5-4. Very balanced, showing he was a versatile player. Laver has 8 Grasscourt Majors, 1 Claycourt Major, 4 Indoorcourt Majors, 1 Woodcourt Major. That's 8-1-4-1. Very lopsided and grass/indoor heavy, showing he was more of a fastcourt player and not as versatile.
I think Rosewall is head and shoulders above Laver, in almost every way. I don't even see it as debatable, statistically.