I just switched to the 630G, after years on an Animas pump with the Dexcom. I will be upgrading in the spring to the 670G. I loved Dexcom, but not my Animas. I just started my first sensor tonight, so I can't address the accuracy yet. I do like that I only have to have a pump in my pocket, instead of carrying both a pump and a receiver.
Someone earlier posted about safety of getting too much insulin. It is my understanding that the 670G actually has two sensors on it, rather than just one. So the two have to be within a slim range of one another before the pump will give/stop insulin.