Since I have been collecting lenses for 40 years or so I have manual and auto lenses from many manufacturers and the Sony A7 appeals since it is tiny and, being mirrorless, has a very short "film" register making it possible to fit almost any lens made using an adapter. I have an adapter which can autofocus 1930s Leica lenses, which is more fun than useful, but hey!
From Canon's first autofocus EOS I bought, a 620, until about 10 years ago I used Canon EOS for most things and a Leica for non-zoom and non-telephoto stuff. In the end I tried others because I was missing pictures because changing settings took so long, particularly going to manual focus for when foreground vegetation was in focus and the main subject wasn't. This eventually annoyed me so much I got rid of my EOS 5D.
If I could only have one camera now it would be the Olympus OM-D E-1, a superb small light camera with a brilliant range of lenses which are also light for their performance.
On a practical rather than geeky side whilst its resolution spec isn't as high as my Sony in real terms it isn't an issue. Firstly only a tiny minority of lenses have high enough resolution to show any difference on a high resolution sensor, and pretty well all of them are the specialist prime lenses very few amateurs use, and then only if using a very rigid tripod on a very clear haze free day. Secondly tests I have done on print resolution show that whilst the convention of 300 dpi on prints is the limit beyond which a finer pitch is totally invisible, for me 200dpi is looks the same unless examining the print with a loupe, which means for 8x10 prints 3 megapixels is plenty
So I think at my age choosing a camera which I actually am prepared to carry everywhere is better than a theoretically superior one which lives in a drawer...
