It makes little difference. If the fixed rate were higher for one of them, you'd want to redeem the other. But, as kupo
notes, the fixed rate is the same.
Since both are less than 5 years old, you'll lose the last three month's interest whichever one you redeem. This means that if you redeemed this month, you'd get the value as of November 2012 for either:
$5,222 $5,000 I Bond with 0% Fixed Rate Purchased August 2011
$5,114 $5,000 I Bond with 0% Fixed Rate Purchased January 2012
Keeping the August bond might be slightly better because its value rises 1.30% from $5,222 in November 2012 to $5,290 in July 2013. The January bond's value rises only 1.25% from $5,114 to $5,178 over the same period. Keeping the August bond you'd also be 5 months closer to holding for 5 years, when the 3-month penalty goes away.