How often do you erase/write data to them? All flash based memory storage devices are prone to memory wear and manufacturers only guarantee file integrity before a certain number of writes.
Personally I have used both. One of my flash drives has been in use since 2007 with no issues and my SD card has only just started to have read errors though removing then reinserting fixes it for now.
Try formatting your flash drive, maybe there is some bad data on it. Also, if you get some of those counterfeit drives that claim to be 8 or 16GB, get a flash memory tester. Some of those drives are actually less than the stated capacity. I bought an 8GB drive and ran the tester, turns out it is only 4GB so I get errors on anything higher than that.
IMHO stick with flash drives.
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