I have the Lowepro AW300 slingshot bag, and I'm very pleased with it.  It holds my two short lenses and two telephoto lenses just fine.  With a top compartment for assorted goods, I can place my keys, wallet, and bottle of water in it, and leave my purse at home when I am out for the day.  The 300 is the largest of the 3 slingshot bags, and it has a snap that comes around from the back near the waist and attaches to the sling, so that it does not swing around when you bend forward, as girsempa said, and helps to lessen the weight on one's shoulders when cinched snugly .  For me, it opens easily enough for changing lenses and can be swung around easily so you can sit in a chair or against a flat surface without removing it from your shoulder.  I had a larger backback type bag but traded it in on the AW300, as it was too bulky and cumbersome, and I've not regretted it.