OK, this is a really good one. A little anecdote:
A few months ago I submitted 4
Barber quarters to ANACS. I considered 3 of them low MS (62-63), and one to be a decent AU. I got back 3 AU58's and an MS63. The one I thought to be AU was the MS63.
Needless to say, that caused me to reevaluate my personal standards for grading
Barber coins.
After much consideration and loupe work, I concluded that the defining area on my coins was the wingtips - that's the only place I could see what could possibly be considered wear on them. Now, here's why your coin is a good one for me.
The obverse of your coin is not as nice as any of my 4. Yours shows either strike weakness or wear all through the right side of the leaf crown, and the hair above the forehead. There's what I believe to be wear at the top of the cap. I may be wrong on both counts.
Here's one of my AU58's for comparison:


Your reverse shows very little wear - I'm believing that there's more detail on the shield than the photo shows - but there's still a touch on the eagle's neck and at the wingtips. Depending on the obverse (is it a weak strike or what?), I'm going to call yours AU50-55.
Oh, yeah - I put my 3 AU58's on
ebay with strong, top-of-the-market Buy It Now's for the specified grade. All 3 were gone in 48 hours, two of them to someone associated with the Bass Collection.
The MS63 hasn't sold in 3 tries.