From Reddit. math is also provided there:

Paladins do more sustained single target dps than warriors.
Warriors have better burst dps and far better aoe dps.
Paladins are better for tanking long term high damage fights such as multiple adds or an enraged auto attack based boss.
Warriors are better for tanking frequent spike damage based bosses which are what make up most of the games end bosses currently, due to big hits taking up less of their maximum HP and being able to self heal for 900-1000 as the hits land which leaves them at much higher max and total hp amounts after each spike. (see post for math and better examples).

My own observation: The logic behind this is that a Warriors main mitigation skill (Inner Beast) should always be up during the "danger" moments that occur a few times per minute. While Paladins do have those massive mitigation skills, they are not always up for those crucial heavy damage moments because of their long cooldown.