The sega-16 link has the information, it's too bad the images are gone now.
The rule of thumb is model 1 has the best picture and audio, model 2 can be ok but are mostly "bad." The Sega CD has its own audio encoder so it solves that problem, and you can use a 32x, which has its own superior video encoder, to solve the video issue if any.
I have three model 2s, and the "best" one has scratchy audio and the video has a faint "grid" pattern to the display. I do all my Genesis gaming on a model 1, non-TMSS. Its only problem is the common "rainbow banding" issue that comes with aged caps in the system, but it's hardly noticeable.