So my guide if you guys want to play the original From Soft games that the Souls series is based off of.
-What is the best From Software first person dungeon crawler?
Shadow Tower.
-I want to play the King's Field series!
Just read this.
www.kings-field.com/history.html
The King's Field games have aged horribly.
-I want to play the King's Field games despite how badly they have aged!
Play King's Field 1-3. They are the main canon. You'll most likely need a translation patch for 1. KF1 in the US was canonically KF2.
-I want something different!
Play Echo Night.
-I want something hard!
You should be fine with everything else already mentioned but if you do want harder, try Shadow Tower: Abyss. Not only is it tough but, to my knowledge, there still isn't a translation patch. You are alone in a deadly and foreign world and don't even know the language. There is nothing that solely depends on needing to know what is said so you can still beat the game.
-I want more!
Play Eternal Ring or the fan made Sword of Moonlight games
My personal list of quality is:
Shadow Tower > Echo Night > Eternal Ring > King's Field 2 > King's Field 3 > King's Field 1
Though ST, EN, and KF2 are easily my favorite. 2 is ridiculously memorable from way back in the PS1 days.