I've got a closet full of packs and tried fitting regular backpacks with insets but, since I usually carry longer lenses, I haven't found any of those setups to be satisfactory. So, I've settled on three favorites for different puposes. The following two, plus a small Manfotto (from Costco, recently) for a smaller lens setup. If I carried smaller lenss more frequently, I would consider the MindshiftGear Rotation 180s. I like the concept and the protection it would afford for skiing. I might break down on that one yet.
For hiking, I really like my Lowepro Flipside. I use the 400 because it'll pack my K3 attached to the Sig 150-500, plus several other lenses and a bunch of accessories, whatever I need. They have other sizes, to suit your kit. I like to add various accessory packs and a lens drop to the hip belt, and the Lowepro is well thought out for that. I also like that I can lay it down and access it from the back. It's quick and clean.
I recently acquired the 560 and carry that with a Lowepro Lens Trekker. This is an amazingly well-built pack, but is expressly designed for a super-tele. The K3/560 combo is relatively light, but crazy long, so this pack works really well. The thing could carry a horse.