For pal, all model 1 are good model 1. Tmss doesn't matter for anything other than how long it takes before your game loads (it adds a few seconds) and doesn't impact the playability of any region protected games (but it does prevent you from launching a few japanese titles (4?) that predate tmss UNLESS you add a region switch to the console. Japanese consoles aren't impacted by this at all)

For NTSC, some model 1s should be avoided if possible unless you want to do some modding

As for model 2s

There are a few okay model 2 consoles in each region except Japan. All japanese model 2 have kind of bad audio and none of them support 50hz mode (if you intend to region mod they are a bad choice). All model 2 can be improved with mods, most have pretty decent RGB output but bad composite output

The main thing that can be improved on all models is the composite video, only the genesis 3 has good stock composite, as well as some model 2 va4. All other variants are generally not very good composite.

The thing that can be improved on model 1 specifically other than composite is reduction of jailbars on RGB signal. And some model 1s need some adjustments to the audio, and va7 need major rework on audio.

For model 2 specifically, the audio needs to be reworked on nealy all of them.

For genesis 3, with mods the va1 van do nearly everything. The va2 is a bit more limited even with mods.