In theory, using the DVI input on a TFT monitor will give a superior display because there is no conversion of signal to be done. In practise, [Normal everyday use] you will be hard pushed to notice the difference.
If you have a graphic card and monitor and both of them support DVI, then yes, use it, But I don't think it would be worth the extra cost of buying a new card. There are no other major differences, the TFT with analogue input still sets itself up automatically and self adjust for best display. j.