hook_user('register', ...) versus hook_form_user_register_alter()

Hello,

I'm updating an old custom module that made heavy use of hook_user, including use of the 'register' operation to inject additional custom elements into the user registration form. It also used hook_form_alter to change the submit button text on the registration form.

I'm now considering switching over to use only hook_form_user_register_alter (a.k.a. hook_form_FORM_ID_alter) to simplify things.

So, is there any reason to prefer hook_user('register', ...) to hook_form_user_register_alter()?

Thanks!
Ben