This is an incredibly tough round. These are probably Metallica's two most popular "classic albums" and every song left is good in many regards. However, I have to vote for something, and my tough choices shall be all of the songs that I give less than 9 or 10/10:
Ktulu - the weakest track remaining from RTL. This one has loads of atmosphere, but is light on variation. Still a great tune, 8/10, but Metallica instrumentals don't do much for me.
Disposable Heroes & Leper Messiah - good songs, but definitely the weakest on MOP. Disposable feels rushed and scattered to me, while Leper is a bit uninspired (other than that post-solo riff - which I believe Dave Mustaine lays claim to).
Orion - stronger riffs than Ktulu, but less atmosphere. Again, great tune, 8/10, but this one could have used lyrics.
I truly don't understand the hate for Thingie. It's a really good, heavy, sludgy song that is incredibly important in the evolution of Metallica. Thingie paved the way for Sad But True and all of Load and ReLoad and...suddenly I understand why you guys don't like it. Meh, I'll hang out in my own corner listening to Thingie and the 90's albums and rock the F out.