Spock had been called a lot of things.
Green blood, hobgoblin, elf, half blood, mixed breed… the list was endless. He also had a lot of titles to go with his name, Commander, First officer, Science officer, Son. He was used to the insults, the labels, nicknames and jeering, but there was one thing he couldn't get used to. Due to his mixed heritage, he had the option of last names. He could follow his human side, and take on his Mother's maiden name, Grayson or he could honor the Vulcan ways and use his Father's age old family name.
Spock used both names. To appease his Father, he was S'chn T'gai Spock. Though part of him resented the name, he used it as a term of respect.
On Earth, he was Spock Grayson. Humans tended to respond more easily if he had both a first and last name. 'Spock' was just too alien in many cases.
After his Mother's death, Spock used his mother's name more and more frequently. It seemed a simple way to honor her and though he would never admit it, he liked the feeling of closeness the name brought.
So Spock had many names. Some he liked more than others. Friend, beloved, companion,but if asked to choose, the name Spock liked best was that of Grayson.