I've gone through a ton of bags. Partly because I was never satisfied with a particular bag and partly because I've grown my kit. Nowadays I just use a 30 liter Osprey Momentum pack. It's a regular backpack and I just throw my gear in with a camera insert or just wrapped up in some way. It's my favorite bag and really the only way I've found to carry all my stuff the way I like.
For my taste the camera bag manufacturers haven't designed a bag that totally fits my needs.
Lowepro's website has a bag finder that's fairly accurate. You input how many body, lenses, flashes, etc and it will show you the bags that will fit your gear.