Miles looks better because he's substantially more productive in the non-shooting phase of his game, but Miles' shooting percentages are completely dreadful and are on a steady 4 season decline. Not the right direction of improvement for a 23 year old player.
I think that if Miles played more with the starters his percentages would go up. Because he won't be the main offensive weapon coming off the bench. Just look at the other 6th man percentages; Jason Terry, Jamal Crawford, Lamar Odom, Rudy Fernandez, Gilbert A. But I do agree its not a great line up to pick from AK, Hayward, Bell, and Miles.