As is usually considered better or more formal at least in British English. However, like was used for almost 350 years as a conjunction before some people realised that it was "wrong" as this quotation from Random House Unabridged Dictionary shows: "—Usage. LIKE1 as a conjunction meaning “as, in the same way as” (Many shoppers study the food ads like brokers study market reports) or “as if ” (It looks like it will rain) has been used for nearly 500 years and by many distinguished literary and intellectual figures.
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