I'm casting my vote for the Saturn.
I love my Dreamcast, and all the great games I play on it. Under Defeat, Ikaruga, Soul Calibur, Test Drive Le Mans, Daytona USA 2000, Grandia II, Skies of Arcadia, Fatal Fury: Mark of the Wolves, Zero Gunner 2, Border Down... great stuff. However, there's simply more on the Saturn that appeals to me.
The Panzer Dragoon series, the copious amount of import-only shmups (some of which are still Saturn exclusives), NiGHTS into Dreams, Sega Rally Championship, Mass Destruction, the best version of Powerslave, Dragon Force, Sega Ages, Shining the Holy Ark, Shining Force III, Vampire Savior, X-Men vs Street Fighter, Marvel Super Heroes vs Street Fighter, Guardian Heroes, Astal, Legend of Oasis, Galactic Attack, Darius Gaiden... it's just too much 2D (and early 3D) goodness.