Whose last name should my child take?

Susanna
I am 19 and pregnant with my first baby. My boyfriend (the baby's father) and I have been on and off dating for about 4 years now. We had all these plans to get married and have a life together, but broke up in November before I got pregnant. We obviously got back together, but the plans of marriage aren't as big. I love him to death and one day I do hope to be with him, but I just want to make sure it will work out between us and we won't break up again. So, if we did ever get married it would be a while from now. 
My question is with all that being said, whose last name should our baby take? Does it matter if we aren't married now? I want our baby to take his because we are planning to raise this baby together obviously and honestly I like his last name better than mine...but I know my parents would be furious. I really don't know what's appropriate. Thanks!