Bradley Taylor

This plugin disables the custom fields metabox that WordPress includes by default. The custom fields metabox includes a slow query, which on large sites can take 10+ seconds.
Do not install this plugin if you rely on the custom fields metabox. If you do not know what this means you should probably not install this plugin. If you are using a plugin such as Advanced Custom Fields, Custom Field Suite or similar to manage your custom fields don’t worry – these plugins will be unaffected.
The custom fields metabox performance is currently being discussed in <a href="https://core.trac.wordpress.org/ticket/33885" rel="nofollow ugc">Trac</a>. If you find this plugin useful you may want to follow that ticket.

Remove custom fields metabox

Remove the custom fields metabox to improve performance.

pixelgrade

George Olaru

Andrei Lupu

With <a href="https://github.com/pixelgrade/pixfields" rel="nofollow ugc">PixFields</a> you can have a custom fields visual manager.
Note: this plugin does not add any style to the output of custom fields. Its just adding metadata and offers a way to overwrite the html from the theme. 
The theme should style the output of the metadata.

PixFields

PixFields offers you a nice interface to add custom metadata into your favorite post type.

Remove custom fields metabox vs PixFields