I'm always striving for / dreaming of wide angle and shallow DOF, so for me, the larger the sensor the better - or a smaller sensor with super fast lens. Unfortunately both large sensor nor super fast lens tend to make for large cameras/lenses, and that's contrary to my other wish: a camera that basically disappears when I'm not using it.
I think the rumored sony 2/3" type curved sensor with a lens of ~21mm f/3 equivalent might meet my minimum criteria for DOF control, and it's obviously very small (smartphone), so if the lens is right, there's no real need for me to have a larger sensor than that. Still, if I were to design a camera/lens combo myself, it'd probably be APS-C at least.
Heh! I've lost my obsession with super wide angles, so that makes my life easier. Having seen what Sony can pull out of a 1" sensor coupled with a stellar lens, I'd be perfectly satisfied with that image quality in atleast 85% of the shooting scenarios I find myself in.
The 1" sensor's DR and resolution are pretty much all I am likely to need, but the fact remains it's a pretty small sensor so for low light, f/2.8 or f/2.4 doesn't quite do it for me, by some margin. Maybe f/1.4?
FF/35mm (Nikon, Leica); size/quality ratio is best for 20MP sensors, though. I just like playing with all aspects of photography, so the more versatile, the better - but at the moment, I draw the line at 24MP because bigger files would clog my processing pipeline and fill up my disks even faster ...