There isn't a 20th century set that IMO is more like the N172 Old Judge set than the Zeenut series. I say this because the key to Zeenuts (and OJ's) isn't really their technical grade but their overall eye appeal, a big exception is the 1911 set which is colected by the grading type. Most Zeenut collectors would prefer a card with a clean image on front with writing, damage, etc on the back vs a card with a fairly cruddy image on front that may grade much higher technically, much like the "photo quality" of an OJ being more important than the technical grade according to most true OJ collectors. Then the overall size thing also has the Zee's and the OJ's unrivaled in their eras...
In regards to your specific question, I agree with much of what Scott posted in regards to Zeenuts.
Of your two cards the 1920 is far and away the nicer of the two. The 1920 set is a popular one and is much harder to find than the 1919 set (which seems to be the most plentiful of all the sets in the 1916-1921 range).
In regards to Zeenuts as a whole the most popular and by far the most common of all the sets is the 1911. That set actually has the possibilty of near completion (unless you need all variations and the Bohne card), something most other Zeenuts don't afford you.
Zeenut cards are VERY difficult to price for many reasons. If someone is looking for a particular player from a set they WILL probably have to pay a premium (and often a large premium) to find that "needle in a haystack" as in many cases the individual cards from any given year are actually quite rare, that being said because of the vastness of the checklists and the overall number of different cards produced almost forces one to collecting them in the form of a type set, team set, a particular year they find appealing, or something along those lines. Very few people are stupid enough (
) to actually try to collect every card ever made because even in low grade trying to collect roughly 4,000 different cards will run you several hundred thousand dollars and in many cases there are only a handful of copies known of certain cards. The point is that finding a single card from each year isn't too difficult because of the size of the sets but going beyond that can be very problematic. The complete Zeenut run has never been accomplished and likely never will as even the most advanced lifetime collectors still have sizable wantlists of cards that literally never come up for sale. IMO one does not truly understand the word "rare" in this hobby unless one has dabbled into collecting some of the tough Zeenut sets.
I know this doesn't really answer your question, but if anyone wants to check out my ever-growing Zeenut accumulation feel free at the following link...
http://www.starsofthediamond.com/zeenuts.html
(I'm at roughly 2,000 and growing...)