What think to be consider when you prefer coding a solution in form of child theme rather then in form of a plugin ?
Themes and plugins solve different problems: plugins are for business logic, themes for presentation. They are not interchangeable. I prefer the right tool for the right job. :)
i prefer in child theme (or in function.php), rather then in form of plugin. It's more easy to reuse. You can just move it from one theme to another.
Depends on the situation. If it's something that could readily be used by any (or many) different sites regardless of the theme, I do a plugin.
If it's something specific to This Particular Site Only, I would probably put it in the child theme's functions.php. Even if specific to the one particular site only, I might make it a plugin if it's something I might want to turn on and off later.
Other than the fact that you can turn plugins on and off, there is little if any difference between code in a plugin and code in functions.php.
If it's something most easily coded straight into the theme (e.g. a particular permutation of the_loop) then of course just do it in the theme template and put supporting code in functions.php