My two cents:
I've been using a LowePro Mini Trekker AW for nine years now.
It's been holding one or two Canon bodies (5D Mk II + 1Dx) and lenses up to 300 mm L ƒ2.8.
This little backpack has been used and abused and despite a few material flaws (one zipper going on strike) it's been better than OK.
And the rain cover (that's what the AW stands for) has saved my gear several times.

The model is now discontinued. Closest current model is the LowePro Pro Runner 300 AW
but since I have geared up a little, I'm about to get myself an F-stop Satori EXP or Tilopa BC.

For bigger lenses, I'll stick with the LowePro Lens Trekker 600 AW.

Cheers,

:: h ::

PS. An odd experience from boarding planes with these two backpacks:
They are well travelled. I go to Africa at least once per year on safari, and sure enough I have been asked many questions by security, most of them being in What is that?-category, but I have never been asked to check any of these items in.
To me it's a bit puzzling, as the Lens Trekker 600 is a rather big thing –.28 x 32 x 65.5 cm (11.02 x 12.60 x 25.79 in).
Either I've been lucky or cabin crews have treated me like if I'd been traveling with an antique violin.

But tripods and monopods I will check in. They travel in a special padded tripod bag.