I just noticed that tmux has some basic sixel support now - https://raw.githubusercontent.com/tmux/tmux/3.4/CHANGES
discovered at https://www.arewesixelyet.com/
discovered at https://www.arewesixelyet.com/
Anyway, Chafa's results are darn good IMO. The images in the gallery don't I feel showcase how well it matches against organic forms. And it handles a wide variety of images. SVG etc.
Even when I have access to pixels, I find on slow connections Chafa can be a decent form of compression :) For example, I was using the ffmpeg patch to play a video remotely to figure out what it was and while I could have relayed it with ssh -YC , Chafa was simply a lot more performant due to it being a lossy transformation. Kinda like playing the video in a VNC session with jpeg loss cranked up to max, but without the need to fire that up.