I've been on both, and think the Parisian version "works better".
I like the Paris Discoveryland theme much more than Florida's Tomorrowland. Tomorrowland and (WDW's Space) was really neat when space travel was a big deal. But, now that the space shuttle launches feel like an everyday occurance, Florida's theme is much less "tomorrow" as "the tomorrow that existed in the 60s when we planned this place." The Parisian park's Jules Verne retro-tomorrowland just works better now that tomorrow is here. (And, as we've seen in Anaheim, trying to overlay the retro-tomorrow look on top of 60s tomorrow just doesn't work.)
That thematic advantage carries over into the Parisian Space Mountain, at least for me. Plus, I happen to enjoy the more aggressive coasters, which gives Paris a further edge.