The second one (the forum didn't keep the file names).
Also note the final version (2.0) was built only 12 days after this 1.6 beta, so unfortunately we won't find much changes
I wish we could find anything older.
Edit: also, considering this beta was generated from a patch (1.6 to 2.0) it could mean these are the only files changed.
Edit 2: According to Wikipedia, the PS version was released in September 1997, and the PC version in October 31st 1997. Versions 1.6 and 2.0 were built in October 10th and 22nd respectively. Judging by the release dates, the PS version shouldn't include the changes introduced in version 2.0. (The bug fix in the final level and that changed Paramonia screen) Can anyone with a PS version handy confirm this?
Edit 3: Notice how the "spike wall" is cut about 8 pixels at the bottom. Seems like it was a quick and dirty last change.