I'll second Topeak just because I like their system and it was an easy install as well. As for the disc/non-disc rack type, I can tell you the only thing that matters is where your calipers are located. On the chain stay? Any rack will work. On the seat stay? You probably need the disc-specific rack if it's available, or be prepared to modify whatever you buy to accommodate the caliper.

If you're going to use panniers, make sure you buy a rack that will keep them out of your wheels.