Which type to use for checkbox fields in hook_field_schema?
A tiny int would be most appropriate in my opinion:

$columns = array(
  'value' =&gt; array(
    'type' =&gt; 'int',
    'not null' =&gt; TRUE,
    'size' =&gt; 'tiny',
    'default' =&gt; 0,
  ),
);


A 'standard' int would be overkill for a field that will only ever hold a 0 or 1 value.

See the Data types docs for an overview of the different types available to you.