Thank you ladies for replies. I guess a darker color will work better. All the measurements are different on various websites so I was confused. I'm leaning towards medium for everyday use, if it doesn't fit the laptop, I'll get a more structure tote like Prada.
I just put my 15" macbook in my medium cuir. It just fits and zips up if the laptop is tilted a bit. It doesn't look good though. The bottom dimensions of the bag are just too small. I would use a larger bag or at least a different shape.