Dreamcast.
For the most part, most of the games on the Saturn are also on the Playstation. There are some great games on the system like Dragonforce, Shining Force 3, Albert Odyssey, etc, etc.
However, the Dreamcast had a ton of great games that were actually original during the time of its release(we know alot of these aren't original anymore due to the rereleases on other systems, but during the release of the system they were.) Crazy Taxi, Soul Calibur, Skies of Arcadia, Phantasy Star Online, Resident Evil Code Veronica, Carrier(decent RE ripoff,) Ikaruga, Lord of the Berserk Guts Revenge, Project Justice Rival Schools 2, Dynamite Cop, and Shenmue to name a few of my favorites.
I guess there's also the fact that I've played alot more Dreamcast games that haven't been on another system than I've played of the Saturn.