Seattle or Rock On The Range Concert

In May I have been invited to go to Seattle with my aunt, uncle, and cousin from May 19-24. I also had told my fiance that I would go with him to a concert called Rock On The Range which is rock and heavy metal. I know some of the bands that are going to be there but I'm not that familular with the music. I think it would be fun to have that experience and to be able to enjoy it with him but my aunt wants me to go to Seattle as a vacation for graduation even though I have already been there once but it is beautiful and theres lots to see.