Personally, I would prefer the fastest time/no casualties/highest score challenge simply because these goals could be seen in the final record. As for no save-file abuse...
To each his own, I guess. I did a no save-file abuse before for Resident Evil 2 (in fact, it's a no saves at all straight run), but that was because for this particular game this unlocked new items for you (it was either a cool new attire for your character or a rocket launcher with unlimited ammo, I forget).
