I'd probably take Ride the Lightning over Hell Awaits - Slayer hadn't quite come into their prime yet. Metallica's next release was Master of Puppets - which was pretty much their peak. And Justice For All... - was great (and I love Garage Days Revisited), but they had lost Cliff Burton. The Black Album was good too - but they were definitely on the down swing.
Slayer, on the other hand, were getting ready to release their seminal Reign in Blood, South of Heaven, and Seasons in the Abyss. They had a bit of a downswing as well - but continued to put out passable albums with some great songs - especially God Hates Us All, World Painted Blood, and Repentless.