Should i build a gaming pc or buy a desktop?

im going to buy a new desktop basically gonna make a gaming set up (new desk, monitors for my xbox one and ps4 etc.)

now i was just gonna buy a desktop from bestbuy either a hp or lenovo but bunch of my friends say build your own gaming pc. Now, i dont really play games on pc i just want a very good performing desktop.

600-700 is what im willing to spend and i want to know should i buy a desktop or build one?

would a gaming pc perfom better than a desktop that i would buy at best buy?

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