Re: The dreaded "can you recommend me a good camera"?
FWIW, I have used the original RX100, and like it a lot, notwithstanding some of its ergonomic and functional aspects that are not as nice as those of some other cameras; I have an S110 but have not used an S120; and we have the much older SX230 HS; but I have not used the others. The G9X gets downgraded for its limited zoom range and mediocre lens.
Wow that hurts. Mediocre lens and the 3x zoom is limited as opposed to the 3.6x of the RX100. Stabilisation is probably a lot better on the G9X as opposed to the RX100.
A good point for the person needing the advice is to remember is Canon stuff does often get talked down routinely on a casual basis with strong descriptions of lesser problems and other brands talked up likewise so look around for all the facts. Of course users get defensive too so no easy way to find out what these cameras are really like.
This site's review of the G9X II, which I'm pretty sure uses the same lens as the original G9X, concludes, "Soft lens greatly reduces detail capture." See https://www.dpreview.com/reviews/canon-powershot-g9-x-mark-ii-review/5. To me that's a pretty serious flaw. Put on top of that the smallest zoom range of the cameras discussed: 28-84mm equivalent f/2-4.9 for the G9X versus 28-100mm equivalent f/1.8-4.9 for the original RX100, versus 24-120mm equivalent albeit on the smaller sensor for the S120.
And yet despite that, I put the G9X as my second choice.
And you know what my biggest reservation about either of those is? That for $368 I can get a brand new RX100 with a memory card and case (https://www.bhphotovideo.com/c/product/1209681-REG/sony_cyber_shot_dsc_rx100_digital_camera.html), or for $429 I can get a brand new G9X II with memory card and case (https://www.bhphotovideo.com/c/product/1321603-REG/canon_powershot_g9_x_mark.html). IMOPO, your friend should stretch the budget just a bit and buy a new camera.
With its slick responsive touch screen interface the G9X would be natural for a smartphone user compared to the RX100. I think one of these 1" cameras would be better rather than the small sensor cameras for a noticeable improvement in image quality.
In my experience, the original Sony RX100 has better overall image quality than my Canon S110, but until you get into very low light and/or print sizes larger than 8x10 inches, the difference is pretty modest. See my post at https://www.dpreview.com/forums/post/61545472.
Finally, over the years most of my compact cameras have been Canons; I don't think you can say I'm biased against Canon. I have owned the A570 IS (actually two of them, for a while the second was my 'car camera'), SD4000 IS, SX230 HS, S95, and S110.