All of the above mentioned are subjective. I honestly don't consider monalisa as the best painting (but I do think Da Vinci was the best painter and Michael Angelo the best sculptor)

Honestly, Imo St. Thomas isn't the best philosopher, I don't honestly have a best philosopher as there are a wide array of topics and there are people best in each. (But, in theistic philosophy, even if I don't agree with Sankaracharya's views (because I am a catholic) but still finds his way of thought better than St. Thomas or any other Western theistic philosophers. I finally understood the idea of Holy Trinity not by the explanation of theologians of catholic church but when I applied a philosophical view of Sankaracharya about Brahman to Trinity)

Best landmark, Christ the redeemer? It's totally subjective and also you can only say among the world only if you have seen all the landmarks.