Well specifically I can give four.
One- The Catholic Church is one and united absolutely under the Pope. It is not a loose affiliation of self-governing congregations and nor is it a composite group of churches led by various Patriarchs.
Holy- The Catholic Church has produced numerous great Saints even giving us the woman who is mentioned today as the very model of selflessness and charity, Mother Teresa. Finally, the very Sacraments and reverence of the Church is also her mark of holiness
Catholic- The Catholic Church spans all cultures, peoples, and tongues. It has a more diverse membership than any other church body in existence. Wherever the Church is dominant she is a uniting factor for the population, sweeping aside differences. This can be seen in 19th and early 20th century America where you had Irish, German, Italian, and Polish immigrants united against discrimination by the Anglo-Protestant majority for no other reason than they were Catholic. Modern America itself is also evidence of this where a Catholic parish will be filled with White, Asian, Black, and Hispanic people. While most Protestant churches here cater to a specific group like Blacks or Hispanics with most being predominately White.
Apostolic- The Catholic Church has a line of bishops going back to the Apostles themselves, something no Protestant church can claim.