Credit history vs. lower debt?

I want to take out a mortgage in about a year, but have little credit history. I have good credit, but no high amount loans.

I will be buying a new car soon and was wondering if it would be better to:

a.) Take out an auto loan so that after a year I'd have some credit history (a 15,000 loan or thereabouts, which I've been approved for) OR

b.) Pay cash for the car so that when I do apply for a mortgage next year I will have no debt, but little credit history with larger loans.

Thanks!