I would pass on the 1st and 2nd gens unless you know how to fix the battery. Red/Blue/Yellow/Green weren't too good (ya, i said it). And Gold/Silver/Crystal were really good, but again, the battery.. Otherwise you'll lose your save data which would annoy me to no end.
Other then that, I'd suggest either emerald or black2/white2, or maybe even HG/SS. Those are the ones I think are best.