E dur in my opinion.It's alot of work, but it's one of the "easy" ones.The middle section with all the sixts, does sound as hard as it is to play.
10 -1 should probably be off the list in terms of easier etudes. I would hope that some of your thinking on selecting an etude though would be based in what techniques you would like to work.10 -3 is probably a good choice in terms of difficulty, and is a very nice voicing study. 10-9 is relatively accessible also but emphasizes different techniques. (the left hand work translates very well into better performances of the nocturnes)
That's what I thought at first, but I'm still having a hellish time getting it up to speed. That not mentioning the phrasing and musicality