I am it's not even a debate........Ljubicic was number 3 in Fed's "era"............
David "mug bendover vulture" Ferrer at 31 yo is currently ranked #4
(However, here's more measured response:
1. Ivan Ljubicic was #3 for only 9 weeks in 2006
2. Fed was extremely dominating in 2006 (arguably the most dominating year in the open era) that he won most titles, with Nadal winning some clay titles, leaving the scraps to the rest, and hence there were much fluctuation in the ranking after Fed-Nadal.
3. Ljubo won Indian Wells in 2010 at the age of 31, during the peak years of Nadal-Djokovic-Murray.)