all USB Flash Drives have a finite lifespan, and if it starts acting up, you'd better backup important stuff to your computer.
i always tell people NOT to make a flash drive your ONLY copy of a file.
even if it's just on a 2nd flash drive, have a 2nd copy of any important stuff.
as for brands, SanDisk created the flash memory we all use, and i prefer their drives.
Kingston is good, too.
but again, ALL USB drives will die eventually after so many writes. even if you take perfect care of it.