I only use Duraloops in my Zebralight. There are regularly good deals at Amazon, search for "Duracell Pre-Charged Rechargeable Batteries" there and they'll come up. Don't pay more than $10 for a 4 pack. Also recommend Costco's Eneloop pack of 8 AA + charger.
The propblem with saying that a Zebralight is "optimized" for a particular battery chemistry is that the nimh and alk have different voltages depending on their charge level. Though the Zebralights can account for this difference and keep your output nice and steady. Also, Zebralight uses eneloops in their literature for output comparison and runtimes.