I haven't used the Superior Auto mode (yet) as I am wary of the RX100 doing unexpected overlaying tricks to increase the dynamic range when it deems appropriate. I should probably experiment with that to see if I agree with what it does.
I can, however, thoroughly recommend using the Intelligent Auto mode as the default setting. You can always switch away to one of the other modes if you think you know better than the camera and have the time and presence of mind to do a better job. But I find it's often the case for travel and general photography that photographic opportunities can be very fleeting and there often isn't the time to consider things like aperture, shutter speed and ISO. So for that reason I generally leave the camera set to iAuto, so it's ready if I need it in a hurry. I find that it generally does a good job.
The Sony online manual - which runs to about 227 pages as a PDF document - gives a brief description of the different modes. Unfortunately, it's not well written and you sometimes need to play with the camera a bit to see what they are trying to say.
Briefly, I think the difference between P and iAuto is that you can change exposure / focus settings within P mode, but within iAuto mode you're telling the camera to do everything itself. iAuto+ adds the overlay trickery I mentioned above.
I can't use center af in this mode. The af point it thinks is right, may not be what u intend. It is what I set the camera to when I give it to someone else to take a picture of my wife and I. I normally use aperture priority or program mode. The thing that drive me crazy about the RX, Nex and a7 family of camera's is macro is a scene mode. So I just leave the last selected scan as macro.. FYI...intelligent plus thru trial will figure in most cases u intend macro mode though.