>>35858388as mentioned in the thread, Crystal has earlier availability for a few Pokemon like Teddiursa, Sneasel, and Suicune. but it delays Ho-oh/Lugia, and doesn't have Mareep, Girafarig, or Remoraid at all.
HGSS adds some cool stuff like a couple new routes, the Safari Zone, restored gen 1 areas, and of course gen 3-4 stuff. but some of the stuff it adds is annoying.
go with Crystal if you like old Game Boy aesthetic and music, or HGSS if you want something newer. that's the really the most important factor.
