My boyfriend and I have a child, we are both filing as head of household. He make about $5000 more than I do. Who should claim the child to get the most back?

Do either or both of you qualify for the Earned Income Credit?

Go to:It's easier than ever to find out if you qualify for EITC (http://www.irs.gov/individuals/article/0,,id=96406,00.html)

If so check the credit table:
Publication 596 (2007), Earned Income Credit (EIC) (http://www.irs.gov/publications/p596/apa.html)

Who gets the most?

Five Rings has it right.

But a word of caution: you BOTH cannot file Head of Household!

ONE of you must file SINGLE.