Avlrc is right that the fullstock may be more desirable, but ultimately you shouldn't necessarily buy what's most "valuable", buy what you like. If the Spies gun is as nice as the one in the second photo with the tang sight, I'd buy that one. I know "buy what you like, not what you think is valuable" is the cheesy phrase they use all the time with the Antiques Roadshow, but a lot of it holds true. Neither of those guns are very valuable the way some original guns are, but each has its own interesting features that make it collectable. Buy whichever one you will appreciate more on your wall.
-Eric
PS - if you're starting down the road of collecting and selling, only once you get good at identifying what's valuable would I say "buy what's valuable, sell it for more, then buy what you actually want".