i've never played the SNES version, but i have played X, GX and that GBA version.
F-Zero X on the n64 is pretty cool imo. the graphics are pretty bad even for the n64, but it's fast even with 30 cars on screen and the handling is better than on F-Zero GX. death race mode was awesome, wonder why they didn't include it in GX.
EDIT - oh yeah F-Zero X had a nifty heavy metal-ish soundtrack :dio: