My experience is there's not much difference between VGA and DVI. I know many people say DVI is better because it's digital, but my own experience is I can't tell much of a difference.
Also DVI and HDMI can look different. I had a LCD TV hooked up via DVI on my cable box and when I switched to HDMI, it looked better. Who knows why. Maybe it was the cables or TV circuitry. The only way to know is try each one and see for yourself.
I couldn't disagree more. I'm a web designer and gamer. If the PC-end is VGA, you'd definitely see a quality difference in your picture by going DVI to HDMI. I can't say the difference will be as dramatic as mine was, but I bet you'll notice.
Example: I have a 42" TV with VGA and HDMI hook-up. My GFX cards (Nvidia GTX260, 8800GT) both show improvements.
HDMI-VGA: At it's native resolution it looked good and text was legible from a distance for the most part.
HDMI-DVI: I got a new cable from a friend and thought I'd try it out. I hadn't done anything like this before and thought the results would be something like hooking up S-Video or something, so I didn't expect much. When I booted up Windows (Vista at the time) and saw the login I literally said "W...T....-" My eyes got bigger as I logged in and saw how vibrant and crisp everything was. Small text, previously illegible, was easily seen from across the room.
*If you can get it locally, don't be afraid to try it out and return it if it isn't satisfactory.