one of the best custom field plugins for devs so far

I used to use Meta Box plugin (metabox.io), but ACF beats it as of now by some margin because:

– there’re no additional extensions to install;
– there’s a lot of documentation;
– the code for defining fields is much simpler;
– a lot of hooks allow you to do anything you want;
– unbeatable flexibility OOB — global fields? menu item fields? user fields? all taken care of;
– UI is very good and flexible as hell, makes content editors happy;
– wide integration with other plugins;
– ACF Pro is freely available on Github for use with those clients which might not afford paying for it (though we do use the paid Pro as well for lots of them).

Some deficiencies as well:

– json sync was a major frustration because of some sync irregularities and problems. Had a talk with support and they were unable to help. Had to switch to PHP export, but that’s actually better since you can also use smart PHP logic which makes a project a lot leaner;
– the Pro price would be a bit steep for novice developers;
– some people from the support team are not very helpful (James Stout), though others do really good job (John A. Huebner II).