Interesting thoughts here.
I will take any good chance at them, but prefer bedded deer.
Feeding you have the noise of the chewing in their head, and their head can be in the brush, somewhat blinding them. Some say they concentrate on eating more, thus making it easier to get close. But I have to disagree, I believe they are much more aware when they are up and about. And they are far more spooky in the open.
The down side to a feeding deer is they move, its hard to move in on a moving target.
The plus to bedded is they are less alert, and stationary. I can spend 8 hours on a buck and know he will be very close to where he was when I put him to bed. I just have to stay unseen, unheard, and cross my fingers the wind works in my favor.