Taxonomy vs Values module in my case
The Values module is a field for users to enter their own list of values in a key-value format.

Core taxonomy module is used to create lists of terms which can be placed as a field on the registration form using a 'term reference'. This would then appear as either a select list, radios or checkboxes (checkboxes if the field is multi select). 

The difference is that with Values, users enter their own values and with term reference and Taxonomy, users choose from your list of terms in the taxonomy. Which do you want? I think if you're looking for subscriptions, it's term reference and Taxonomy.