Rhystic Study is an awesome card draw spell, but there are other strong ones
Whenever an opponent casts a spell, you may draw a card unless that player pays 
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"I'll teach you the leyline paratrigonometrics, no problem. But you need to show me how to make that fiery swirly thing." —Zimone, to Rootha
Here are 22 cards you can replace Rhystic Study with in your deck.
Mystic Remora
Very similar to Rhystic Study. More conditional (only triggers from noncreature spells, worse in causal), and it dies after couple of turns. However it is harder to interrupt, and way lower CMC.
Insight
Rhystic Study at home. Fraction of a price, with a fraction of the power. Nice alternative if many of your friends play green. This one is not a game changer, so you can include it in lower bracket decks. Unconditional draw is a plus.
Consecrated Sphinx
It looks similar at first glance, but it has downsides. High CMC, and it gives opponents more window to react (they are not likely to cast draw spells if this is out, they will remove it first, many of commander decks pack cheap creature removals). You will still draw from people starting their turn, unconditionally.
