I have good luck with Yellow Spanish onions. They store better than any thing else I have grown. Big Daddy onions keep well, but not as good as the Yellow Spanish.
Walla Walla won't store hardly at all. If refrigerated and they will last a couple of weeks. Their best use is for early and sweet fresh onions.
Successful onion storage depends quite a lot on conditions. If the humidity is high, they won't store well. Here in dry Utah, they store pretty well in a mesh bag hanging in the basement. My basement has an almost steady temperature of 68--70 degrees and a relative humidity of 40--45 %. I will have some onions keep until May.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-