NPF pf difference

[rhino64%epost.ch@localhost]

Hi All,
     Could you Please indicate me what are the main differences
between the both packets filters NPF and PF?

Until now I use regularly (under OpenBSD) PF to create
firewall. What I appreciate particularly with PF is the "overload"
function and the "authpf" shell.

I have not seen any mention of equivalent functions in NPF.

For what reason does one choose NPF over PF (or PF over NPF)?

Any idea would be greatly appreciated.

Thank for your help,

Kind regards,

rhino64