Daerr boxes used to be quite sturdy, but since Daerr was taken over by another company the quality was reduced IMHO. The material looked quite windy to me, so I opted for the Touratech panniers. Since then I've done 50,000 kms, very often rough roads (Southern Africa, Australian outback) and dropped the bike several times. They still look fine, though heavily scratched and slightly dented ;-)
I fitted the Touratech rack as well, which I would have taken anyway, even with other boxes. I reckon it's one of the best racks on the market.
Apparently the boxes from Metal Mule are very robust, but I havn't any experience with those. Besides, the're quite expensive.
Only when we pause to wonder
do we go beyond the limits of our little lives.