Interesting discussion given the differing viewpoints set forth.
Of particular interest to me is the question of whether APS-C is "caught in the middle".
For me it is not.
I started digital photography with a small sensor 'tough' camera (before that term was coined) because I wanted something that could survive in the sometimes unfavorable environments in which I find myself, living in the mountains and taking advantage of what the mountains and wilderness offer. I still have that great little camera, still use it, and I am still impressed with the quality it can produce.
But there are limitations on what can be designed into a camera the size of a deck of cards that is waterproof, shock resistant, crush resistant, etc.
I decided to go to full frame. I bought a Nikon D700 DSLR along with 24-85 and 70-300mm lenses. My first outing with it I was photographing a cruise night at a nearby annual car event. I was using the 24-85 lens and panning the cars as they moved, pressing the shutter button at the right moment. About 1/2 hour into this I turned to my wife and told her this was the best camera I had ever used. Besides the image quality, I really liked the feel of the camera itself. The weight was very similar to my film Leicaflex and Zeiss Contarex SLRs. In other words, stout.
But that was a lot of gear to carry, certainly compared to my little 'tough' camera. I started to look for something that would bridge this considerable gap.
Around this time Sony introduced the Nex system, initially consisting of the Nex 3 and the Nex 5. I thought the Nex 5 with the (original chrome) 18-200mm lens would, as closely as possible, equal the focal length range of my two FF Nikon lenses.
I was extremely impressed at the results I derived from this much smaller and lighter system. So much so that I parked the FF system. I will never get rid of the FF system. It is now obsolete, but just as capable now as when I bought it. I just don't like to get rid of really good gear.
That Nex 5 18-200mm system has been on numerous trips and has always delivered stellar results. The only limitation was that the included flash sits so low on the camera that it is useless with the 18-200mm lens because of the size of the lens barrel. The Nex 5 has no hot shoe, so an additional independent flash unit is not possible. A few years ago my bride decided I needed to be able to do fill flash. So I bought the then current Sony @6300 body, on which I mounted the 18-200mm lens. I also bought a Sony flash unit tall enough to clear the lens barrel, so I can now do fill flash. That left the Nex 5 and the 18-55mm lens that came with it. For the first time I put that 18-55mm lens on the Nex 5. I found that the Nex 5 flash would clear the lens barrel, so then that system was able to do fill flash. That flash unit is very compact, and folds down, so I leave it on the camera.
I am averse to changing lenses in the field. I leave the 18-200mm lens on the @6300 and the 18-55mm lens on the Nex 5. Even though both are the same format, the Nex 5 with the 18-55mm lens is smaller and lighter than the @6300 body with the 18-200mm lens. I now have a choice of two Sony Nex/Alpha systems to use. I decide which to take dependent on what I will be photographing. Both deliver outstanding prints at the maximum size my Canon printer will deliver, which is 13X19".
Some may contend that APS-C is caught in the middle. For me though, I think it is an ideal compromise.
