Recommended module or method for a generic map/media embed field?
The built-in text area field seems like it would be sufficient, assuming that this field would only be accessible to trusted user types (see "Tread with Care" later in my post).  If you configure your filters to allow "Filtered HTML" (with embed/iframe allowed) or even "Full HTML",  users can just copy and paste embed codes to their heart's content.  

Any HTML snippets that are posted will get rendered when viewed without needing any extra template code or a custom module to handle them.  A "Filtered HTML" filter might still strip important attributes away, but "Full HTML" will not.

There is not really a generic way I can think of that would allow you to verify (even if you felt confident about your PHP) that iframe/embed html is a Vimeo video vs a banner advertisement vs a reference to malware.  That is why there are 20 different emfield modules; the sources for each type of content all do things differently and can constantly change how they approach embedding.

Text filters are available at: /admin/config/content/formats (in Drupal 7) and full documentation can be found here: Specifying the allowed formats for user input

Tread with care!

Keep in mind that users will be able to post anything else they want, too.  The "Full HTML" filter offers minimal protection and even if you went with "Filtered HTML" instead of "Full HTML" and permitted iframe or embed tags you are still in potentially dangerous territory if this field is going to be used by just anyone in your userbase.

Example/Demonstration