I was in school there during the Rankin days. Olah and Rankin were pretty equal. Pardon is frequently far better, but has also disappeared or fouled out over his whole career.
Pardon has fouled out 8 times in 101 career games, never more than twice in a season. Olah fouled out 7 times in 122 career games.
I was an Olah fan, too, but Pardon's career rebounds average is 6.9, the same as Olah's best single-season average. Pardon has averaged a full point more, .1 fewer (i.e., equal) blocks, and fewer turnovers. He's also a career 61% shooter from the field, while Olah was around 48%, and the eye test to me at least says Pardon was a more effective defender. (I'd love to see @Styre or someone break down other data out there.)
Olah was a productive and often unfairly maligned player for us, but I'd take Pardon over him without much thought. (And Olah over the other post-Esch choices just as handily.) On the whole, we've had 7 straight years of pretty competent and dependable center play, and unfortunately it's at best a toss-up whether that will continue next season.