Two slams. No contest. The #1 ranking is seriously getting overrated by some on this forum, especialy in this era where it has literally turned into a joke of late. It is one thing to argue two year end #1s in a row like Wozniacki might have close to the value of 1 slam win (especialy had 1 of the 2 not been an all time joke like Wozniacki's 2011 year end #1), but to just say so and so randomly reaching #1 at some point, not even ending a year there or spending much time there, is close to on par with an additional slam title. Please, give me a break.
2 slams also proves you are not a fluke, which in this era of mug #1s also has produced alot of 1 time winners out of blue that look almost flukish, unlike in the past where 1 slam winners were people who contended for so long, usually just beaten by the greater players in the end, but thankfully got that 1 slam atleast. So in that sense a 2nd slam is an enormous thing, way beyond the value of spending 10 weeks at #1 at some point in some year.
If Ivanovic is your example, well Sabatini, Novotna, Martinez >>>>>> Ivanovic both in careers and as overall players, and they all never reached the #1 ranking and also won only 1 slam. So I guess that emphatically answers the poll question. Holding the #1 ranking and 1 slam doesnt even automatically make you better than someone who only did one of those (well atleast the 1 slam part only), let alone as good as people that win 2.