I currently have a lowepro orion trekker II. I like that it has a separate section for odds and sods, mainly so I can carry bits when I'm out and about with my kids.
but I find the compartment at the bottom is a little small when I'm carrying anythign other than my 50D + 24-105 + 85 1.8. I can just about squeeze a 50D+70-200f4 in there by removing most of the dividers, but nothing else.
I'd like something that would let me carry the 50D+70-200f4, OR 50D + 100-400, and still have space for my 24-105 and 85 1.8.
I've looked at the slingshot AW200 which seems a little narrow across the back. should take the 24-105 but I don't think it'll take anything much longer. is the AW300 much wider?
the daypacks seem similar to my orion trekker - some space above, but again the camera section seems small.
The big lowepro backpacks probably have enough space for the gear, but nothing for personal space.