Posted the following in another thread but figured this one was probably better.
In and of itself DVI and Component cables are NOT better or worse. Now, having said that. In most cases a DVI connections from a satellite should be better but not always. Here is the reason.
Information on todays downlink satellites is sent by digital streams and not analog. The STB then has to convert the digital to analog to put it on the component cable, then your TV (if its Plasma, LCD, etc) converts that analog signal back to digital. Dependent on the electrical components in your STB and TV there could be a loss of data from those conversions. Which then leads to a loss in picture quality.
With a DVI connection the STB and TV does NOT have to convert from digital to analog because the DVI cable is a digital connection.
So....if your STB/TV is VERY good at the conversion from analog to digital and there is no interference that may cause problems on the component you very likely won't see a difference in picture quality. As mentioned in this thread, when using your DVI the picture is not aligned (off to the left an inch or so) then the TV is not converting that digital signal correctly and would need to be resolved by the TV manufacturer.
The same works the other way, if your CRT is not good at converting a DVI signal to analog then picture quality will not be as good as say component.