Best reissue or older version of Led Zeppelin 4 in vinyl.

My go to copy before I bought the Classic Records pressing ia a German re pressing distinguished by a yellow sticker with a white exclamation point affixed to the record cover. Sounds Uber.
Whoever did these did an excellent job on this series. I also bought Neil Youngs After the Goldrush and The Yes album with the same sticker and well they are my go to copies to this day.

Discogs is also another huge wealth of info and buying selling.

You might want to search out the George Piros and George Peckham ("Porky") mastered reissue from the mid-’70s. The Monarch pressings (a plant that is now regarded in hindsight as having pressed a lot of good sounding records) tend to be bombastic, though a little noisy. (For Atlantic records, you should be able to see "MO" as part of the catalog number on the label, in addition to certain deadwax inscriptions). If you are careful to find a clean playing copy, you should be "in" for your budget.
As to "best," that’s often a matter of personal preference. And it usually comes with a price tag these days.

Thanks to all for your input. 

@mental ,
I own that set.

@pivetta,

OK, I realize your $50 spending limit is a crucial issue. This IS for one lp. So I say, why limit yourself to one lp when you can now get "How The West Was One", box for a little over $100? Is it that important that you have the perfect copy of "IV"? You’re likely on a lifelong journey that will never be complete.

As for SH forums... they suck. Ever tried to eat a biscuit with nothing to drink? I rest my case.