Originally bought the 10.1. It's a fantastic tablet but the lonnnnng charge times was kind of killing the experience for me. Was always needing to charge and it seemed like it was always dead whenever I needed it.
So when I read the 12.2 has USB 3.0 (like my Note 3) I bought one in hopes that the charge time was shorter. It's much, much shorter - somewhere around 1/4 the time. That was really my only problem with the 10.1 so the 12.2 is absolutely perfect for me.
I prefer the size of the 10.1 but now that I'm used to the 12, it's really nice too - and actually better for taking notes and drawing. I'll probably go back to a 10" screen someday since holding the tablet in one hand is more convenient. However I'm absolutely *loving* the 12.2. One of the best gadgets I own.
For me the speed differences between the two are negligible.