I personally prefer Nikon, because it gives nice contrast to the picture. I use to have a Cannon, it has a good sharpness but its picture looks lifeless compare to Nikon. Go with Cannon, if you  dont bother to use the photo editing software to correct the colour or else Nikon is better.

I think Sony is also a good choice. Its easy to handle and its not that expensive now a days and its sleek too.

And sorry I've no idea regarding Olympus and Panasonic.