Impossible to determine. Both have feats that go far beyond the normal limits of a ninja.
Naruto has an immensely abnormal life force for a ninja, but died instantly to Kurama's extraction. Kushina, in comparison, not only lasted for a long time against something with instant lethality, but also made some incredible feats of power. (binding Kurama and making a barrier Hiruzen could not break through)
Tsunade, on the other hand, survived being bisected, and could even do summons, which requires a lot of chakra.
What we have here is a contest of natural hardiness VS artificial heartiness.