Matrox is the king of 2D. Few would argue about that fact.
Personally, unless you need the extra features of the G550 and most people don't, then I'd look into the G450. It's cheaper and offers comparable 2D quality.
If your using DVI-Output then any card will do, 2D quality using DVI will be very similar regardless of what board you purchase.
If your using the regular VGA out, then I'd look into Matrox if your going to be using 1280x1024 or higher. Below that a decent ATi/3dfx/Appian board should offer comparable quality.
If you intend to run at 1600x1200 or above then I'd definitely strongly lean towards Matrox though.
Personally, I find Matrox vastly superior at 1600x1200... and if you intend to work on the system for 4-6 hours at a time then I'd bet you'd really miss Matrox's quality.
It's always important to remember the monitor, cabling, connector can also have a huge impact on 2D quality. Individual eyesight can also come into play.
I've seen some swear their perfectly satisfied with MSI/PNY nVidia boards at 1600x1200... even though MSI/PNY are typically thought of to have among the worst 2D quality. Whereas others I've heard will swear up and down that they absolutely cannot using anything but Matrox as soon as they bump the resolution above 1024x768.
If 2D is the only factor then Matrox is king, and they well deserve their sterling reputation for image quality above all else.
16/32MB OEM G450's are widely available at prices between $65-85.
is the g550 worth the extra few dollars for 2d quality and DVD decoding?
While Matrox has the 2D quality crown, I'd much sooner look towards ATi, or SiS for DVD playback. The GF4 MX would also be worth a glance.
If you wanted the absolute highest DVD playback quality then the Parhelia would top the rest, but DVD performance would would be very close between the GF4 MX/ATi/SiS. ATi's got the best DVD visual quality besides the Parhelia.
The G400/450/550 can offer pretty good DVD image quality, certainly better then most but they won't match up to ATi in that respect. DVD performance is rather mediocre from the G400/450/550... but that shouldnt be a factor at all unless you expect to be doing other rocessor intensive activities while playing back a DVD.