if a screen can display 16.7M colours; 1 LED screen has 50M:1 dynamic contrast the other LED 30M:1 -> what's the difference? both can reproduce the same amount of colours; different contrast = different colour, am i right? so im asking -> is there even a difference?
Well contrast ratio is the amount of light emitted by the brighest white vs the darkest black. So 10:1 would mean a full white pixel emits 10 times the luminescence of a full black pixel. High contrast ratios would typically indicate bright colours and deep blacks.
They're talking about dynamic contract ratio there, which is something to be disregarded - just marketing crap. While static contrast ratios (could be 700:1, 800:1, 1400:1, 2000:1 at best) are vaguely worth considering, there's little consensus on a standardised method of measuring dynamic contrast ratios. Rapidly auto-adjusting the level of the backlight from frame to frame produces the dynamic value, whereas static contrast ratio is based on a single, still image.
If you want a quality TFT display, the most important factor is panel type. Most TFTs use TN (Twisted Nematic) panels with poor quality (vastly inferior to that of old CRTs) and serious colour shift along vertical viewing angles. Choose a monitor that uses an IPS (In-Plane Switching) panel for good colour quality and consistency. You can pick up some 23" examples by LG for around £150. Better still, Dell actually make excellent quality displays (believe it or not) if you're willing to pay a little more.
Best advice would be to shortlist some IPS panel TFTs in your price range and then get professional reviews from CNet, Anandtech etc. Like with quality audio hardware, what makes a really excellent monitor can't be boiled down into numbers. Would make things simpler I know, but it's something worth properly reading up on!