Some SEO folks used to believe that you could gain some small amount of relevancy by placing your keyword in a BOLD tag rather than using it in a STRONG tag.
In actuality, Google’s Matt Cutts says he was shown the piece of code in Google’s algorithm that says <b> and <strong> are viewed as the same in the algorithm. The same goes for italics <i> and emphasis <em>. See for yourself at the 50 second mark in this video:
Of course it’s important to keep in mind that this video is 4 years old!
My opinion is that since <strong> is the newer tag, you should use it over <b> within any new content you may be developing. I don’t think either is better from an SEO ranking perspective but in the future if a decision is made to change, it makes sense that the newer tag would be favored over the older tag.

