I always knew of the link:. Never ever heard of link+:. The webmaster tools are of Google is very useful and provides lots of information about your website. But I don't know why the link: command doesn't show up all the links to my site and on the same end webmaster tools proper link for that website. My recommendation is to use the one in webmaster tools. The link: can also give you a good idea about the websites you don't own and you can't access their webmaster tools area. Really interesting ones worth using.