I have, over the years, had shoulder bags from Hama, Lowe-pro, Tamrac and Gilles Berthoud and never quite liked any of them.
Some of them have been too flexible in configurations, so that they lose their shape after a year or so, others have not been flexible enough so that they have been less than ideal for the stuff I want to carry.
I think it was about 1994 I first saw a Billingham 550 in use, and was impressed by how it shaped itself to follow the waist and back of the user. I put it out of my mind because they cost about as much as a used 400/5.6ED.
In 1997 on tax-return day our local hasselblad store had a 550 ex-demo bag for a good price since they wanted to sell bags, not just display them. I bought it, came home and started filling it. By moving the Superflex inserts around I got it to balance and be easy to carry with 2X F4E, 2X SB-24, 24/2.8, 35/1.4, 50/1.8, 55/3.5 Micro, 105/2.5, 80-200/4.5 and 180/2.8. There was still room for cleaning supplies, extra battery packs, a brick of agfachrome and some rolls of HP5.
It behaves more like a messenger bag than a traditional shoulder bag, in that it pulls back on the shoulder rather than outwards-downwards. That makes it easy to carry even fully loaded.
I still use it when I have to have everything and the kitchen sink with me, and a backpack is out of the question but it *is* a bit large.
I therefore got a 206 to carry one body, a wide zoom, a normal zoom and a flash. It is still as easy to carry because of the shape, only smaller.
Sometimes the 206 is a bit small, so for event photography I got a 335 that takes the same as the 206, but also has room for a 35/1.4, a 50/1.4 and a 85/1.4 for available light.
The bags have proved themselves to be very water resistant and durable. Another thing I like is that they don't look like camera bags.
I will post some pictures of the bags later.