The gray Eagle LE Courier Bag is excellent and discreet, lacking tactical tells. I've used mine with great success in non-permissive environments. I think I posted a review or pics of mine here once. Recommended.
On a large metro university campus recently, I couldn't swing a stick without hitting a Timbuk2 messenger bag. It was as if they had given them away or air dropped them. If you order them, you can customize the colors to suit.
As always, access to your gun when off body is slow and requires two hands, one of which may not be available. All fall short in some way, and there aren't really any that truly distinguish themselves for speed/ease of presentation.