How tall are you?
If the cabinet is yours, make it so it's comfortable for you. If it's for when your friends come over and everyone plays or your wife likes to play, then you'll need to split the difference.
Tip: If you make it more comfortable for her, you'll get to keep it in the living room longer

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In general, measure from the floor to your elbow when you are standing straight. Then subtract 2 to 4 inches.
For reference, a Defender cab is almost exactly 42" from the ground at the front of the panel. Galaxian 37" (Seems a little low and it makes me want hunch) and a Crystal Castles is 38 1/2". The Crystal Castles seems to be the most natural for me.
RandyT