i have found the key thing with svideo is if u use a really high quality svideo cable, its makes a big difference (and keep cable short if possible, eg. 1 meter or 1.5 max)
im using a really well shielded/quality svideo cable and did some comparisons between mame using my laptop->svideo cable->tv... and then, my ps2->rgb scart->tv
the only difference was the colours (and sorry but even that isnt a big difference). if anything call me crazy but the rgb for me looks almost 'too' good. i prefer a kind of beaten up slightly blurry arcade monitor look, and svideo gives me that much better than the 'perfect sharp' looking rgb setup
ps. using quality svideo cables eliminates all interference, and all dot crawl also (well, also the tv u are using needs to be able to handle/convert/display svideo well, but most modern tv's are good at that anyways).
so, in my opinion, dont let anyone tell u that u need rgb. svideo is great if u use high quality cabling. using poor cables tho u end up with interference, dot crawl, maybe colour bleed, and perhaps washed out/dull colours.
EDIT: here's a pic below of my svideo image on my tv. note that the digital camera has added some 'wavy interference lines' and has made it appear more blurry than it actually is (actually, i have to be honest and say this isnt even an svideo picture. this is a composite video image (ie. 2 of the svideo pins are tied together and sent to pin 20 of the scart connector. so its safe to say, svideo would actually look better than this))...
