The G6 shoots tack-sharp photos, has RAW format, uses CF cards, has an IR remote control, and a nicer manual focusing control. The S2 has that long zoom, some special effects, electronic view finder, takes superb video, and has image stabilization. The G6 has a faster lens, but the S2 has a faster processor. I've got them both, and just pick whichever one suits the particular situation I'm in. The S2 will never have the photo quality of the G6, but the S2 can grab photos that the G6 can't. That's about it. They're not interchangeable, and therefore really aren't comparable (except in price). Think about which one fits your needs better (the most often). I had the G6 first, and if I could only pick one, for me it would be the G6.
Remember you're out about another $50+ for the Maha C204w charger and a few sets of 2500mAh batteries for the S2, while an extra G6 battery is about $15. Pro 1's are cheap now, too, just to throw in another choice.
Regards,
Dean
Lutz, FL
G6, S410, S2