If you can use a DVI-HDMI that would be better because both are digital. I don't think it would be an issue going from VGA to HDMI because the PC should be able to do the resolution without problems, right? As long as you can do 1920x1080 @ 60 Hz you should be fine.
I can't speak of the ST30 or S30, but you'll be hard pressed to find an LCD this year that can match the picture quality of the UT50, especially in its price range. Most people on AVS who have commented said you'd have to get something like the Sony HX 929 or something like that. Way out of the price range to the UT50. In the price range of the UT50, I don't think you can get the picture quality mainly because the introduction of the LED-lit panel. In my opinion, they're trash for picture quality and you'll be hard pressed to find a CCFL LCD.