For me it depends. But also I like to optimize my gear, rather than maximize it.
When I travel with medium-format gear, it will mostly be with a backpack. That is the most comfortable way to carry the weight. The bag I use is an Osprey Farpoint 40, which works well as carry on, but over the weight limit. My lenses are on a pouch and belt system which allows me to take them out while I am working. The belt is nice because it distributes the weight around my hips.
I also have a Fuji X system. That fits in a Mountainsmith Tour lumbar pack, that works as a shoulder bag as well. I have actually been using that more. The weight of the medium-format is getting me down, so to speak. The freedom of the lighter and smaller system as been really nice. It is certainly more spontaneous and, if you can keep your discipline, just as rewarding. It also lets you shoot in far more situations, not that I have not used big camera in all kinds of situations, but today places and others believe that large cameras equal commercial photography and will ask you to stop.
The last time I went to Tokyo, I took my MFD system and shot for 30 days straight. For that particular project, urban landscape, it was the right choice. But I was exhausted at the end of it. Part of it was the weight, part of it was how slow it was working with the style, which required a lot of tripod work--I have used MFD handheld, but smaller cameras are better for that work. However, I am traveling more for work and the Fuji is far more practical. I am sure I could figure out how to take a MFD system, but there is more to photography than just hauling equipment.
These are the questions I asked myself--what is the characteristics of my images that I enjoy the most? What contributes to the quality I enjoy? This is where technical criteria only work to a certain point. The small stuff we photographers seem to stress over, noise, resolution, dynamic range, etc., where not the deciding factor. When I looked at some of the medium-format work I had done in the past, smaller digital cameras compete on many different levels. They are not the "same," but rather reflect the characteristics of the quality that matter when standing alone, especially when printed (100% monitors views are just not a condition with which to judge photographic quality). This is when I started thinking about how to optimize my equipment, rather than just maximize it.
And part of that is not feeling like a donkey...