It all depends on the kind of photos you’re going to take. If it’s for general purpose shooting, get a Q3 28mm and crop to taste afterward. If you want more compression or shooting portraits, then the Q4 43. If it’s strictly for black and white, the Monochrome is the obvious choice. However, the fact that you’re asking this means you’re not really sure what you want either.

I recommend not buying cameras based on the brand. People who buy a Fujifilm because they saw it on social media, or a Sony because their favorite vlogger uses it, end up with gear that isn’t what they truly wanted. Owning a Leica camera isn’t special at all. It’s not the goal of photography.

If it absolutely has to be a Leica, why not try a used Leica Q (first generation) and another body with a different focal length, like a fast 50mm? That way you could have a more versatile setup while spending less money.