HDMI or DVI are digital. If there is a problem transmitting a signal, the
result is "snow" on the screen. But otherwise, the transmission method is
"lossless". The byte value calculated by the GPU, is exactly the same
when it is clocked into some digital circuit in your projector. So the
quality is not affected by the transmission method (up to the point that
the signal is no longer sufficient to be clocked by the receiver chip).
That is unlike the other, analog methods, as those will lose something
along the way, from video card to receiver.

When you use a VGA connector, especially at high resolution, the sharpness
of the image can be compromised. A video card with too much EMI filtering
just before the connector might only give a sharp picture at one of the
lower resolutions. A really long cable might soften the image as well.

S-Video has a bandwidth of about 4 MHz, which means text won't be readable,
even at 640x480.

So at least in my own case, S-Video would be my last choice. If VGA or
HDMI/DVI are options with the projector, I'd try those before using
S-Video. But with all the devices you have at your disposal, and the
limited number of inputs on the projector, you have to pick and
choose, which device will be using which port.

   Paul