I can't really chose. I love them both. Christmas Eve is more of a mild day filled with the Christmas anticipation feeling. We have little kids and try to make Christmas eve magical without being overwhelmed. We try to keep Christmas Eve to just out little family (hubby, me our kids and my mom as she lives with us) Santa does make his rounds on Christmas Eve on a firetruck handing out candy canes to the kids. It's a very nice calm day.
Christmas day we host breakfest - my dad and his wife come over for that. The rest of the family comes over later in the day and stays for dinner. We pretty much have a full house all day on Christmas.