You don't need to join them all but they are a good start. Which one depends on where you plan to hobby as they are regionally based. Many ladies accept them and it keeps you from having to give your information out over and over. Check down a few threads for more information.

They tend to be geographical in nature.

On the east coast date-check seems to be prominant. Others can share where the others have relevence. I do know that my date-check profile/refs. have saved EVERYONE many headaches.

are ladies who will see new hobbyists without reviews.  Just be sure not to give out any personal information that could get you burned (depends on your job and other factors).