The 8Bitdo N30 Pro Controller is really popular because it's supported by the Nintendo Switch. For smartphones, I recommend the IPEGA Wireless Bluetooth Game Controller because you can snap your phone right on top.
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The video game emulation experience isn't complete without a USB gamepad! I recommend this gamepad: Logitech Gamepad F310 (it's not featured below because they don't allow product embedding). It's a nice, solid gamepad with a smooth grip and 11 buttons.
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