The fact that Freeza survived a genki dama that Goku thought would finish him and kept fighting at max potential a while later, while Vegeta was already half-dead upon being hit with it tells me Freeza's durability is superior. Plus, although he had less plot-shield during his fight with say Zarbon, being utterly trounced by him left Vegeta unconscious and near-death while Freeza's been able to shrug off punishment from people more than twice as strong as him (SSJ Galu vs. 50% Freeza), which all in all tells me Freeza has the edge even with physiological differences in mind.