From what I've gather,
Invidia = Somewhat less expensive, but decent quality. One of the best bang-for-your-buck exhausts out there.
HKS = Makes high quality, but somewhat expensive cat backs. Their older style downpipe was similar to the stock blank plate design, but I think they recently came out with a bellmouth style, but I haven't heard much about that, but it's probably good.
DC Sports = Don't really know much about them
SPT = Makes a decent quality cat back that won't void your warranty. Average price I think.
Cobb = Makes high quality downpipes and cat backs, but you'll pay for it.
Basically, just get a cat back that you like the looks and sound of. I'd stick to any of the major brands and avoid cheap eBay knock offs so you avoid exhaust leaks and fitment issues. As far as the downpipe, any name brand bellmouth style should do.
For what it's worth, I have a Cobb catted downpipe and an HKS Hi-Power Carbon-Ti cat back and I love them both.