I would definitely recommend signing up to more than one of these link companies as each have different adverts that will appeal to different consumers and when people start to recognise the link they may stop clicking or stop taking part in the advert. So to ensure that you have a good variety to choose from then click and sign up to the following links. 1st Sign up, 2nd Sign up, 3rd Sign Up, 4th Sign up.
Where you can post
Everywhere! There are plenty of social network sites and forums that you can become accustomed to. Twitter, Facebook, Linked in, Digg, Youtube, Tumblr and any chat forum that may interest you or is relevant to the link. Even a simple "add me on Facebook here" posted on twitter can be very effective. So be creative with your links and just get posting!!