White hat is all that is allowed by the search engines.Black hat is all the sneaky strategies to trick the search engines. Black hat will not survive for long term, as search engines update their software often and will penalize you and ban you for life.
For many keywords white hat seo will be very difficult in order to rank any site. If you are going to use blackhat software or services, make sure its acting like humans!, you dont want to post 10000 of the same comments in 10 minutes, Google is not stupid they can detect that!!, so make sure its realistic, how much would a human person post per hour? 50-100, then use the blackhat method to post 50-100 in 1 hour. Trust me people are very tempted to do 1000,s of link building because they think quantity is better than quality, THINK AGAIN!