Not too familiar with the stuff mentioned, so I'll do my own:
Piece of Time vs. Unquestionable Presence
Both A+ albums, but Atheist's sophomore is the clear winner. It is without a doubt the best technical death metal album ever made... Okay, maybe it's tied with Nespithe. But compared to Piece of Time, Unquestionable Presence capitalizes on every strength and eliminates just about every weakeness found on that album. UP's rhythms are jauntier and its harmonies more dire, its solos sound less like slop and are actually critical parts of the song, and the already tight musicianship is pushed even further. Every single riff on this album is captivating, whereas there are a couple of bog-standard speed metal riffs on Piece of Time. Unquestionable Presence is something of a standby album for me, its something I can listen to no matter what mood I'm in; Piece of Time is a great album but I have to be in the right head space. Lyrically, both albums are great. While Satan/occult and death/killing are cool, I wish there were more free-thought themed bands like Atheist. Long live Atheist! Reminds me to give Jupiter another go, the plastic production seriously turned me off but I'm willing to try and look past that.