I really like the Fogg and Billingham bags. I have an old Fogg Matriarch that I got on eBay that I use for the S2 and two lenses...works great and is not too big. Great looking (if you like that look, which some certainly don't!), and very very well made. For a really comprehensive kit, the Billingham 445 or 545 are superb, but they are large, and frankly carrying that much kit on your shoulder for a significant amount of time is neither fun nor productive. Billingham does have the best shoulder straps and balance of any sling bags I have used, but even they can't prevent the fact that you are putting all the weight on a single point on your shoulder, which is not the best way to do things! They are the best to work out of, however, so if you work out of a car, or if you are going to a location and then taking the bag off and will work there, they work superbly well. Another great benefit of both Fogg and Billingham is that their bags are waterproof, but not technical looking. You can carry them in most situations, and they will be appropriate. They can look expensive though (particularly before you have had them for a few years!), so that can be a downside. And of course, they look expensive because they are.
If you are going to have to carry the kit a long way, a real backpack is much better. The Gura Gear Bag is pretty good (I have it), but I found the RPT Photo Backpacker system much better for actually lugging things. It is all about emphasis...Gura Gear is a photo backpack with lots of dividers that has been arranged to carry better, while the Photo Backpacker is a high end Kelty hiking backpack modified to accept gear (particularly LF, but it works well with any if you get the divider kit. I bought the Gura Gear for travel, but I found I never used it because you can fit ONLY camera gear in it...it is completely full of dividers, with no space for anything else, such as a laptop. I think they may have changed that now, but in the days of a single carry on, if it doesn't carry a laptop and isn't flexible to carry other items, it doesn't go with me. Simple as that. The RPT is of course too big to be carry on, so not saying they are comparable in this way.