The monitor would look sharper since it has a higher density of pixels. ~2 million pixels (roughly how many pixels are in 1080p) spread out across 27" is more dense than ~2 million pixels spread out across 39". The difference in image quality really depends on the distance you will be from the display as well. If you are playing from across the room on your couch, for example, just go with the bigger display. If you are gaming at a desk or something close, go with the smaller display since up-close it will look better than a larger display.