A credit balance will report as a zero balance.
General drift on the forums is that the highest score results from two or three national / bank credit cards. "Less than half" but at least one reporting a balance, and rotate which ones report a balance each month. Keep utilization below 10%.
I remember one post where the OP did what you're doing, took all to zero balance, then let one card report a small balance and the score went up slightly.
BK7 Filed 8/11/2009 Discharged 11/23/2009. Purchased new home 4/11/2012
Starting Score:11/16/2009 EQ 566 11/16/2009 TU 538
Interim Score: 12/27/2012 EQ 683 09/17/2012 EX (lender) 670 1/01/2013 TU 701
Current Score: 11/06/2013 EQ 708 11/06/2013 EX 702 11/16/2013 702 11/06/2013 TU 729
Goal Score: EQ 740 EX 740 TU 740
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