Replacing My G12: G7X MkII, G1X Mk II or ?

I had the S95, G9x mark II and G1x mark II and still have the G7x mark III and G12. FWIW here are my thoughts:

G1x mark II: The best image quality of the bunch by a long way in terms of detail, noise (lack of!) and gradation. And that is despite having fewer pixels than the G9x ii and G7x III. It has an excellent fast lens and every feature you could possibly need - if not all that you might want!It has a hot shoe that takes a flash or the optional EVF. I had the EVF but I hardly ever used it because of the trouble of getting it out of my bag or pocket and attaching it. It is, however, a very good EVF, with much more resolution than the rear screen. If you want an EVF (and they are useful in bright sunlight) I'd advise looking for a camera that has one built in. Its 1.5" sensor is intermediate between APS-C and micro 4/3 and is huge compared to the 1" and 1/1.7" sensors in the others. This gives it much more ability to render out of focus backgrounds than any other camera here. Drawbacks are a slow frame rate in RAW and it is too big and heavy for a pocket camera.

G7x mark III: The fastest frame rate of the lot and lacking only a hot shoe and EVF in the feature department. Surprisingly, at its wide end the lens is softer in the corners than the slower lens of the G9x II. It is also surprisingly larger, heavier and less pocketable than the G9x II. One would not think 100g and a few fractions of inches could make such a difference. At low ISO (up to about 1000 ASA) the old G12 and S95 match its noise performance and (to my eye) deliver marginally nicer looking images.

G9x mark II: Along with the older S95 the most pocketable. A respectably fast burst rate and feature set, with IQ a little better than the G7x III at the wide end and hardly any worse at the long end, though of course it is a slower lens with a narrower range of focal lengths.

G12: Considering the tiny size of its sensor it competes surprisingly well against the other cameras here. It has the most traditional controls (dials and buttons for everything). It has a hot shoe (like the G1x mark II, but lacking in the G9x II and G7x II) and is the only camera here with a fully articulating screen, though it is not touch sensitive as on the later G- cameras. I think it is the nicest to use, and the older CCD technology shows less noise in expanses of colour such as blue skies and red cars than the newer CMOS designs, despite their larger size and features like BSI and stacked sensors. That is true up to around ISO 800. Beyond that images get rather noisy. The biggest drawback for me is the size and weight. At a little over 400 grams and boxy in shape It is only easily pocketable in an overcoat in winter!

S95: This is basically a simplified G12 in a slim, light (<200g) easily pocketable body. Like the near-identically sized G9x II it is a camera that is no trouble to have with you all the time. The IQ is identical to that of the G12. Among the simplifications is the single central focus point but that is no problem if you were brought up with film cameras where there was no choice but to focus (with the aid of a split prism or micro-prism) and recompose.

All five cameras can produce beautiful images. The older cameras get noisy at high ISO and shoot low-res video by 2019's standards, but if you don't intend to shoot in really dark conditions they will do the job. The main differentiators between the three more modern cameras are size and weight, sensor size, frame rate and lens. But they come at a much higher price than a second hand S95 or G12 and if you do not need the high-ISO, extra pixels and modern features thenthey are not going to give you significantly better images.

If IQ Is your top priority then the G1x II is far and away the best choice. Ignore all those stupid reviews that complain about the fiddly twin rings on the lens and the lack of DR. All they show is that the reviewers didn't take the time to get familiar with the controls and don't know how to expose properly within a camera's limitations.

For pocket-ability the G9x II and S95 are tied, but the later cameras is the winner because of its greater versatility.

For me the G7x iii is the best compromise between IQ, focal length, lens speed, frame rate, features and pocket-ability. It is temporarily a pain that none of my post-processing tools supports the new CR3 format yet. If you work with JPEGs that won't be an issue. Otherwise you can convert the CR3s to DNG with Adobe's converter and then import them into the post-processor of your choice. You can do some RAW processing in the camera, but what you can do is very limited. Or you can use Canon's DPP. It does a good job, but on my averagely-powerful laptop DPP is just too slow.

I have never used the G1x mark III. With its limited lens (f/2.8 max, narrower range of focal lengths) it did not appeal and, perhaps it ought not to matter, but think it looks rather silly, whereas the G1x mark II looks modern and classy. In its favour the mark III weighs significantly less than the mark II and it has the EVF built in. I think you just have to handle one to decide if it suits you. You cannot decide on the basis of tech specs and other people's opinions.

Of course to add to the confusion, there are always Fuji, Sony and Ricoh to consider, amongst others.

I hope this helps.

EDIT:

Whoops. Just noticed that the originalpost was March 2018.  Still, this might be helpful to someone else.