Personally I like to fit the scope to the rifle. Example, my Browning Microhunters have Burris Short Mag 3-9 x 32 scopes on them, my fuller sized rifles (700, M-77, #1, etc) carry Leupold or Burris 3-9 x 40s and my 'little' Marlin Guide Gun has a 1-4x Bushnell Shotgun scope on it.
If your shots are normally <100 yds you may even want to opt for a 1-4X scope.
But like the prev post - all other things being equal, the 40mm objective will extend your shooting time a couple more minutes each day.