Without casting aspersions, let me put it this way:
The
ONLY SD cards I buy are SanDisk. I've never had one fail (and I have 256MB and smaller cards). I've gotten a reply to an email sent on Sunday evening before I woke up on Monday morning. You can talk live to their techs (upper right corner of
SanDisk microSD Tech Support). They're an easy company to work with (if you ever have to, which should be never - I've called them on non-"my card doesn't work" matters. They actually sound as if they care.).
Samsung? I've never used one and, from what I hear they're pretty good. How easy the company is to deal with varies.
Unnamed cheap cards? Sorry, if I had data that was worth so little, I wouldn't bother copying it to a card.
Cards are cheap, data is expensive.