Freesync — keep it on or off?

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Hey there i have a ViewSonic 24″ 144Hz 1ms 1080p FreeSync, ColorX Mode Gaming Monitor HDMI, DisplayPort XG2402 currently. when i have it on its “fps settings” it turns off free sync but on the “moba setting” it turns it on. i mostly play call of duty and val so fps games but i am confused on witch setting to keep it on.
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