You should answer your own question after analyzing serveral proposals instead of going for a single answer. Many people may recommend their own linking service saying it's the best, but only when a number of persons confrim it echoing that opinion, you will find it is really.
I would suggest do a reasearch through Google, and checking people's reviews to find what it's considered the best one.
I agree with the others. Have a look around the web, ask more questions and then make an educated guess. I have also heard of a website that you can get backlinks from, I think it is a backlink builder actually called social monkee. I have no direct experience with it though, so in all honesty I cannot recommend it but I would recommend checking it out nonetheless!