Dreamcast > Saturn > Sega CD (most games I'll just flush)
2D games are about equal between DC and Saturn, but DC stands out with much better and more original arcade ports (especially 3D), devoid of all FMV garbage.
If you're completely into imports, it'd be a tough call between Saturn and Dreamcast as Saturn saw many more releases in Japan, you wonder why Sega failed Saturn in US.
I'm almost done with US DC and started getting back into Saturn (just a little), since we're at trough stage of economic cycle, many games are at bottom low prices, some are beyond my belief.