Given you are in credit building mode (as opposed to score maximization), no harm in letting balances report on one or both cards each month. It won't matter either way. The key point is demonstrating responsible use of credit to build a solid payment history. Never pay late and PIF all statement balances to avoid interest charges.
Note: Staying under 9% AG UT can be challenging - particularly if one only has two cards with relatively low limits. Aggregate utilization in the 10% to 19% range is considered responsible, just not optimal for scoring. So, an excursion above 9% AG UT has no negative credit building consequences if PIF practices are maintained.
Fico 9: .......EQ 850 TU 850 EX 850
Fico 8: .......EQ 850 TU 850 EX 850
Fico 4 .....:. EQ 809 TU 823 EX 830 EX Fico 98: 842
Fico 8 BC:. EQ 892 TU 900 EX 900
Fico 8 AU:. EQ 887 TU 897 EX 899
Fico 4 BC:. EQ 826 TU 858, EX Fico 98 BC: 870
Fico 4 AU:. EQ 831 TU 872, EX Fico 98 AU: 861
VS 3.0:...... EQ 835 TU 835 EX 835
CBIS: ........EQ LN Auto 940 EQ LN Home 870 TU Auto 902 TU Home 950
