It is best to save it to multiple locations if you value them.
I'd be more confident of CDs being a safer bet than flash drives, but nothing is fault-proof. Best to ensure when one develops a fault there is somewhere else you can get a further good copy from.
Personally I would buy an extenal drive and put the photos and anything else of importance on that, they have come down in price a lot lately and are a good investment,
A CD can get a fault making it unreadable (a scratch for example), a memory stick can be easily lost, an external hard drive can stop working or be stolen etc.
I bought an external hard drive over a year ago and now use it for everything. But I have still copied most of my photos on to a DVD, and put that somewhere apart from everything else. That is the secret when archiving stuff....don't keep your copies in the same place as your PC...the same fire will wipe out both !