Most Influential Thrash Metal Album

Which album out of the four above was more influential to thrash metal? I'd say Master of Puppets with Reign in Blood as a close second. How about you?

Master of Puppets may have been influential to other Thrash or Speed Metal bands, but I think Slayer's influence reached far beyond just Speed Metal. Show No Mercy could be said to have helped invent Death Metal by fusing elements of Punk/Hardcore, NWOBHM, with nihilistic themes to create the heaviest form of metal anyone had yet heard at the time.