Well, a week ago I would have advised you against getting an SGS3, but now, i think my opinion has changed. HTC, for some reason, provides absolutely no support to the dev community. Samsung on the other hand go crazy. Unlocked (not unlockable, UNLOCKED) bootloaders, providing devices to the CM team, hiring Cyanogen himself, quick updates and the best thing - releasing kernel sources before the device is officially launched (read that once, can't find a link though).
The other thing is that - under immense pressure of having the 2011 device of the year, competition from the One X and the will to screw the living hell outta the iPhone, Samsung HAS to deliver. The Galaxy S3 will probably be the face of android for the next six months. It'll be the device that everyone will think of when they hear "Android". Tech sites will go crazy reviewing it. Apple fanboys will pee their pants when they see a friend with an S3. If samsung fails to deliver, then HTC One X will keep it's throne, and Samsung will incur heavy losses and mockery from everyone. I don't think samsung will let that happen. After all, they seem to have become the no. 1 mobile manufacturer