Since it's difficult to know exactly which cards will appreciate the most in the future, why not simply build a nice collection, one that you will enjoy. Try to stress quality and buy good looking cards in the best grade you can afford. Focus on different sets and eras (some 19th century, tobacco, candy, gum); try to get Hall of Famers, or complete sets if you prefer; and probably not too much should be invested in postwar cards, since those are baby boomer driven. If you want to collect one postwar player, try Jackie Robinson, since he has transcended baseball and has become an important figure in American history.
In general, quality collections that are built and kept over a long period of time usually do increase in value. Whether they will outperform stocks, bonds, or precious metals I haven't a clue, but you should at least enjoy the project as you go along.
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