For your this question, i will say that there are many services providers in the market but select only those which have good team and which has good reputation in SEO business. It also depends on your budget.
The company should have
– Good team of submitters who have good knowledge of category selection
– Already in SEO business so they do not submit in redirect linking directories
– They should use good SEO friendly directories
– They should have good reporting system
– No automatic software submissions
– All submissions by hand as per directory guidelines
The main point is that they are aware with SEO and not only team of submitters who take some money and submit your website without any results