Last three TFT monitors I've owned have all had both DVI and VGA and I literally couldn't tell the difference between the two (which I tested with both leads connected at the same time so windows thought I had dual screens and then swapping back and forth between them using the monitor input controls). Also my LG LCDTV has a fantastic picture through VGA, every bit as good as through HDMI.
Of course if the content is protected (for instance a retail blu-ray film playing from a blu-ray drive) and your video card and screen both have HDCP then you will need to use HDMI/DVI, but otherwise the difference between analogue and digital is very small if not negligible. You might see a noticeable difference if you go right down to the bargain basement end of the scale, but any vaguely decent screen should have a capable VGA.