Billingham Hadley Large for me, and a Lowepro Pro Roller X200 for big jobs.
The Billingham fits:
A Mamiya RZ67 Pro II D medium format body, three backs and two portrait lenses.
A Canon 1D X, one spare battery, three portrait lenses, two flashguns and a trigger.
A Canon 7D mark II, three spare batteries, one wildlife lens, a thermos of tea and a sandwich.
A Fuji X-T1, an X-T10 and an X100S, one spare battery for each, general purpose three lens set, two flashguns and a trigger.
In addition to any of the above, one pocket always has general cleaning tools, a ColourChecker Passport, spare AA and AAA batteries, spare memory cards and a couple of varieties of USB and FireWire cable.
The Lowepro is for when I want to take two sets of those kits (e.g. Mamiya + Fuji) as well as either up to six flashguns or two continuous lights, or if I'm spending one night away. (More than one night does require packing a second bag, you can't fit a decent suitcase worth of clothes into the Lowepro.)
I will say that, though the Hadley Large does a good job of holding any of my typical kits, it's not exactly comfortable to carry. The shoulder pad—which they have the nerve to not include as standard—is still really rigid and the bag doesn't hang in a way which is comfortable. Nothing else will fit everything, though! The Mamiya's what really does it. Just too damn big and too square to fit in anything else. When Fuji release a 70mm f/2 and a body with a resolution over 30mp, I can finally sell that monster and get a smaller bag, properly downsize. Doesn't look like that will be for many years, though.