Apparently the Florida version has recently been extensively trimmed, killing any speed the ride used to have...
Nevertheless, as I haven't ridden it with the new trims, I'm going to go with Orlando's Space Mountain. I love how compact it all is and how snug the seats are, it feels like you're really flitting around the track with an out-of-control feeling.
I do like California's version (which was pretty much identical to Hong Kong's), but it feels slightly more drawn out and predictable than Florida's.
Paris definitely has the worst version, with a launch that barely makes it over the hill, a few dull inversions and a generally rattly ride.