He's using DVI, so for the most part it should be a mute point as to which has better 2D visual quality... their pretty much assured to be almost identical.
Similarly DVI + LCD mutes the advantage of Matrox's GigaColor.
There isnt a whole lot a manuifacturer can do to improve the visual quality offered through DVI, as it's a purely digital interface.
Pick SiS, nVidia, Matrox or whomever you wish and they'll all be near identical with DVI.
Resolution scaling may differ slightly but that's about it, and in that respect ATi would probably be incrementally better but even there I can't imagine the difference would be much at all.
Given the above I'd be more concerned with what board offers the best feature set.
Matrox certainly has the most versatile and complete MultiMonitor implementation, so if that's of interest you may wish to consider the G400/450/500 for Dual Monitor or the Parhelia for Tri-monitor.
Perhaps even the pricey G200/400/450MMS series if you desire four monitors.
Appian also has quad-monitor boards, but thei implementation isnt quite up to par with Matrox's.
ATi's will provide you with the best TV-Out implementation on a driver level and a very impressive hardware level implementation as well. To back that up they've also got the most fully featured DVD playback implementation available, and it's also well supported by most consumer DVD apps.
If either of those features are needed you may wish to look towards ATi.
3D performance on a consumer/Pro3D basis is evidently a non-factor for you so I'll ignore that.
ATi's AIW 8500DV is worth mentioning as a multimedia board that offers almost anything you could desire.... SPDIF, DVI-I IEE1394, RF Remote, TV-In/Out, digital video editing, TV-Tuner etc.
It's got everything one could desire with a robust software suite to go with it.
Matrox's G450 e-TV, and nVidia's Personal Cinema are also viable alternatives but neither quite match the sheer breadth of options and versatility the 8500DV provides.
The Parhelia loses much of it's reknown if your using DVI, but shouldnt be ignored either.
It'll offer DVD playback quality that's arguably a notch above even that of AT.... though the performance and support isnt near ATi's level with DVD.
As mentioned above it'll provide for an extremely versatile and fexible multi-monitor implementation that can do near anything that's yet been conceived of.
nVidia... is well, nVidia.... they offer fine boards but when ignoring 3D they don't truly "lead" in anything at all so your best off passing on them.
All of my above comments are basically ignoring the cost factor, as you stated it's not a big concern.
If you just want a cheap board that will offer DVI and good quality and an all-around option the Radeon VE/7000 is hard to beat,
DVI, a good Multi-Monitor implementation, fantastic TV-Out and DVD playback capabilities, and will offer nice quality all around.
It's widely available and pretty cheap also.
It's not a gaming card, but if gaming doesnt factor in it does everything very well and it's quite cheap.
Has deservedly won a number of accolades, and OEM support.