I went through this same decision process. I ended up getting the Harmony G-XT, as I needed to be able to create some fx presets that I could toggle on and off during performance. My primary needs were reverb, delay, doubling, and octaves. And I thought the Tone might be useful.
There are tradeoffs! The Create gives you autotune (which can be used as a nice effect now and again if used correctly), and an optional footswitch jack for more control). And megaphone telephone type stuff. It will NOT give you octaves, though, at least not to my knowledge. If you must have octaves, get the Harmony. (BTW, the octaves sound much better than I expected, and I am a stickler for live sound quality.)
The Harmony doesn't have a jack for external footswitch control, but it gives you excellent sounding octaves. Both provide the same tone control (which is a bit limited in my opinion, as you can't tune parameters such as eq or compression), reverb (nice but can't tune parameters), and delay (also nice, but this is where I really miss the ability to set delay time and feedback, etc). And they both do doubling.