Having a mtg or auto loan does help but you also should have a healthy mix of cc's. letting at least 1 cc report a balance is deemed ideal.
For me, my mortgage loan (Oct) basically had little impact on my score on EQ and TU, but my EX score tanked. I cant definately say thats the reason since I have 0 balance on all my cards and last time I pulled that was actually listed as a negative only on EX but the amount the score decreased makes me think that the mortgage loan contributed to the drop.
From what I read on this forum, my score will increase once a good pattern of payment is reported on my mortgage loan. Im going to try and leave a nominal balance <9% on one of my cards and see what that does.
If it does, then I don't need to keep a balance on any of my cards to increase my CS.
It's not an either-or thing. Every factor matters. Low utilization and a mix of credit will help your credit score -- among other things as well.