which is better for security in order to disable login to an account, setting the shell to false, nologin or null?

is there any difference?

I assume that it's not a standard user account that you are wanting to block access to, since you could easily delete it or just do a 'usermod -L [username]' which will lock that account(-U will unlock it).

I believe that the best course of action would be to view /etc/passwd and see what other accounts of that same type are set as and mimic that configuration.

Using the -L/-U option, you will be able to see that the account is locked by looking at /etc/shadow. There will be an "!" in front of the password hash for the account if it's locked.

yes I know how to lock an account, I guess what I am really asking is what the difference is functionally between the 3.

ie is there a way an attacker could get around one or something like that?