It depends upon your circumstances.
For example, if you're being plagued by offers from rubbishgoods.com, blocking '
[email protected]' won't stop you getting mail from '
[email protected]' or '
[email protected]'. You would need to block the domain, so that nothing with '@rubbishgoods.com' could get through.
However if you're getting begging letters from
[email protected], but your girlfriend's email address is
[email protected], you obviously don't want to block Pauper's domain (because you'd also block mail from your girlfriend). In that case you should block just the individual address.