I'm with Lumens - there is no perfect bag, so I've turned into a bit of a bag junkie.
There are a lot of camera backpacks out there, unfortunately their feature list and capabilities are quite diverse. I found some with great storage and access but inadequate support, lots with great support but limited room, and very few that allow one to carry both camera gear and a lunch or sweatshirt. I messed with a few swing-around packs for quick access to camera body and most were awkward to use. Combining this with thin straps and small buckles and the list narrows significantly for those needing a serious camera (and other gear) backpack. The Clik Elite Contrejour works perfectly for me, but this is overkill for many. It swings around for quick access via a side pocket, and gear entry is from the back rather than top or front. It ticked all of my marks.
So I then decided to check out a shoulder bag, something small like a messenger bag that carries just enough gear but forces me to be selective. I didn't like, didn't want a shoulder bag but after using a Think Tank Retrospective it's become my favorite bag. They're a bit pricey new but used bags come up on ebay frequently for about $100. If you don't need a backpack these are perfect.
My third bag is a Tamrac Evolution pack. Not the greatest for hiking but good for lugging lots of gear from place to place.
For each of my bags, and a Think Tank pro speed belt, I use Peak Designs' Capture Pro camera clips. These attach to either belt or pack strap for immediate access to gear. Very convenient, and has mostly eliminated many of my previous requirements for quick access to camera and lens.