I'll probably go for Heart Gold at first, since Gold was my first 2nd gen game, but I'll definitely pick up both eventually.
@Mithosfall: I sure hope so, although from what I've gathered in my travels on teh intarwebz, Game Freak has already integrated some of the old Crystal exclusive content, like the free Dratini you get in Dragon's Den, into HG and SS. Of course, one would hope that this means lots of totally new exclusive content for the Crystal remake.