To come up with a list, I took a look at Federer’s head-to-head at Slams against Nadal and Djokovic to see what his most impressive wins were. I was specifically looking for instances where he beat Nadal or Djokovic after they had won their first title at one of the Slams. He has only two of those wins - Djokovic at 2012W and Nadal at 2017AO. Otherwise, after Nadal and Djokovic won their first Slam titles in Melbourne, Paris, London and New York, Federer lost all other matches against them at those Slams.
So, I guess I would pick some of his toughest Slam final wins to round out the top 5 - he had 5-set wins in the finals of 2007W, 2009W and 2018AO - I would leave the Cilic win out. Winning the FO happened only once and so, I would put the 2009FO final as the 5th most impressive Slam win after the 2011 FO semi. You could put the Sampras win in 2001 over the Soderling win, but to me the fact that Sampras never won Wimbledon again and Federer did not win that Wimbledon title in 2001 makes it debatable in my mind - it took Federer two more years before he won a Slam.
2017AO final - Nadal
2012 W semi - Djokovic
2007 W final - Nadal
2009 W final - Roddick
2009 FO final - Soderling