As far as I know, the latest is Beta 4 for all devices except the iPhone 7/7 Plus, which are the only devices to get Beta 5 (presumably to deliver the network fixes that were a part of the 10.0.3 update that also went only to the 7/7 Plus.)
I tried to do a SU from 10.0.3 this morning, and it still didn't work. I manually downloaded the 10.1 Beta 4 for the 7+ ups file from Apple and installed via iTunes. Worked very well.