I second the rolling backpack recommendation. I'm a big fan of these bags, but I'm careful when choosing one, particularly about weight. I generally only use the backpack function when practicable, as in stairs, rough pavement, etc.
The problem with rolling backpacks, as mentioned elsewhere, is the added weight of the handle and wheels, which depending on your age and physical condition can be really limiting for long use, unless you're a strict "light packer", which I'm not.
I've been using the High Sierra Rev for a year or so, and found it to be a pretty reliable bag. Not too heavy, durable, and carryon friendly. However, if I know I'm going to have to use it as a backpack for any appreciable length of time, I'm pretty careful about how much I load in it.
I've also owned a couple of other High Sierra rolling backpacks, one with a detachable daypack, which for me was too heavy to use as a backpack with both units attached. But the single unit rollers have been fine.