Which is the best registration options?

[ForceHSS]

You need to tell use what spam plugins you have and what group, new members go into if default members group what are the settings of it. I use Spam O Matic not really to stop spam, but for other reasons ie it will send new users to a new group I made that has limited posting and it will auto move them when they reach 10 posts and I have it set up so they are not aware they are in a limited group