I prefer manual link building because you will be able to customize each link. You can also check how the links will look like before you submit them. There will be less errors using manual link submission.
It is better to avoid auto submission or the use of software, in SEO manual link building gives you good results.
Manual submission is the best. It's alot of hard work but it's worth it at the end of the day. Don't by any software that does this. It doesn't work.
Manual is better, but it's rather time consuming, that's the only disadvantage. But hey, you're not earning anything if you're lazy.
And most submission software trigger the red flag from the search engines. Manual submission is time consuming but worth the effort. Don't think that you can rule the web without any hard work.
I'd always go for manual link building. It looks more natural to the search engines and you can also vary the anchor text, descriptions etc. You can outsource to a directory submission service but no doubt there are very mixed results when it comes to the quality of the service.
manual link building is better than all any other mechanic link building tool. Though tool save your time on big amount but does not give much profit as your website deserve.
automatic link building needs you be more careful, if unlucky, google may thougt you use black-hat ways to do seo. so the most security method is do it manually.