I was kind of leaning towards SG because of the new characters and the boost it would give to online and now hearing it has a good grapple character may have convinced meSG is younger, but Third Strike is more popular so you'd probably get just a little less than SG would. Online is going to be very busy for SG in the future, though. There are five new characters on the way so the online scene is going to be very active from now on.
Third Strike has Alex who is pretty cool and SG has Cerebella who is pretty much the ultimate grappler.
I've been meaning to pick both of these up for ages now but never got around to it