With a new Mastodon album coming out, I guess I should get around to their three most recent albums, then!
To give my thoughts on the albums I am familiar with thus far: Remission is my favorite Mastodon album so far. Leviathan has a couple awesome tracks, but overall, while it's definitely good, I wouldn't call it great. Blood Mountain is really good, and has a lot of great tracks. Crack the Skye is really good except for The Last Baron, which is still good, but I rarely find myself finishing it (the same can be said about Hearts Alive from Leviathan as well).