I've been using Meta Box for a large and complex website and felt compelled to publicly share some things that makes Meta Box unique (based on personal experience) compared to other similar WordPress plugins. I've extensively used ACF, PODS, Toolset & CMB2 (100+ hours each), as well as smaller plugins and I've also built my own native WP metaboxes.
- MetaBox has a unique media view ('image_upload') which is a hybrid between the media modal and basic uploading. This allows end users to edit attachments (ex: images) metadata without certain unwanted aspects that come with the media modal. For example, the media metadata is more prominent in this view, and is easier for users to view and update.
- MetaBox has the most out-of-the-box options per field. When I say "out of the box", what I mean is "easy to adjust". For example, you can adjust Select2 and other JQuery options natively!
- MetaBox's Custom Fields UI plugin's interface is amazing and unique. I love how it seamlessly integrates MetaBox plugin features.
- Creating your own custom fields in MetaBox is insanely easy. Other plugins throw around the word "easy", but with MetaBox it is the truth.
- MetaBox either is tied for or has the most filters and hooks (I'd argue it has more).
- MetaBox either is tied for or has the most fields (I'd argue it has more).
- MetaBox has the most complete documentation. Some of your might notice that the help forum is considerably smaller for MetaBox than a couple of competitors. I'd think that is partially due to the completeness of documentation and lack of ambiguity.
- Other competitors claim that theirs is the only plugin you need, but that's actually true with MetaBox (with the paid plugin package).
- MetaBox is much more flexible than any competitor for the reasons I described above and then some.For example, front end form looks are flexible with columns plugin and the templating.
- MetaBox has a ton of unique integrations. For example (although I haven't used it), Composer.
So, in my opinion, Meta Box is hands down the best metabox plugin for WordPress, and it doesn't come close.