Okay so I brewed some pale ales. My house is cold so I had them in water with a fish heater for three weeks to carb up. My choices are they can stay at 50 in the back room or in the fridge now. Where should they stay?
Put one in the fridge for several hours now, then check that it has indeed carbed up nicely. Once they've carbed up, it's recommended to keep them below 60*F, so either of your locations are fine.
once they are carbed the temp for the most part doesn't matter. just keep them below 80F to preserve the flavor. warmer temps will help speed conditioning.