I've heard often that it is better to su to root rather than log in directly as the root user (and of course people also say that it's even better to use sudo). I've never really understood why one is better than the other(s), insight?
The inference is to only
sudo when required.
Most everyday tasks don't require a root shell. So it is good practice to use an unprivileged shell as your default behaviour and then only elevate to root when you need to perform special tasks.
By doing so you are reducing scope for dangerous mistakes (bad scripting, misplaced wildcards, etc) and vulnerabilities from any applications that you use. Especially those which connect to the Internet - see the old adage "Don't IRC as root".
sudo is often recommended because it allows you fine grain and audit the use of such privileges.
By observing these practices you are also in a position to disable remote root logins. This increases the bar of entry for any would-be attacker, as they would need to compromise both a regular user account that was a member of the "wheel" group and ideally only authorised by SSH public keys, then the root account itself.
If you want to create an audit trail, and don't want to fall victim to the "sudo su -" or "sudo vim foo.txt" problems mentioned here, you can use "sudosh". Hand out root access via sudo, but make the only allowable command to run "sudosh".
sudosh is a logging shell, and you can replay the whole terminal session at a later date, showing exactly what the user saw on their terminal.
You should practice security in depth.
Disallow remote root access (or at least root access via passwords). (if you allow root access via keys, carefully control those keys, or better yet use something like kerberos that allows centralized revocation of keys).
I'd disable su and use sudo. That way, users use keys (preferably encrypted) to access the system then they use their password only for privilege escalation. You can restrict which programs people access with sudo, but mostly you just restrict access to who knows the root password.
In an ideal world, you should be able to publish your root passwords on the internet and it wouldn't matter, even if you gave people access to your machine (but didn't put them in the /etc/sudoers file). Of course, you shouldn't publish the root password, but the idea is that you protect your systems with concentric layers of protection.
If you are using root on a regular basis then your permissions may be wrong or you may need to grant sudo rights or a new group rights to r/w/x the files or directories.
Good permissions schemes are something even long-time Linux users get wrong, or don't realize the scope they have.
Don't even get me started on what Ubuntu did!