The prof is quite famous (lots of publications and even a Wiki page). His doctoral advisor is also quite famous (still is part of the faculty of the university that I want to apply to). Would a recommendation letter have a significant impact on my application?

Alternatively I can get a letter from another prof which will be probably a little stronger. Which option would be the best for me? Basically would the other prof's letter carry more weight since he got his PhD from the university I am applying to.

I am applying to a top 3 institution, (if that makes any difference).

Thank you all in advance.