Unless you want / need the rear panel serial port, rear panel IR input, the fiber HDMI connection, or the rack mount ears, I wouldn't suggest going with the HR21 Pro over the other options. I have 3 HR21 Pro's, but I got them because I was integrating them with a Crestron control system and the rear panel ports make that much easier (and the serial port connection could be made to the normal HR21 with a USB to serial port adapter). I'm also planning on replacing my equipment cabinets with new cabinets with rack mount capabilities, so the rack mount ears will come in handy.
The cosmetics of the Pro are a bit nicer than the non-Pro model, but it's not that big a difference.
Besides, if you want the latest, wouldn't that be the HR22?