I've been asking myself this very question as the cost of coins goes through the roof so will the temptation for others to try and find ways of getting their hands on them. I currently have mine in a Bitcoin QT wallet (encrypted of course) with a backup saved on a USB in case the HD fucks up. I'm not really up on all the different schools of thought on where is the safest place is to be honest, personally I like knowing they are on my computer but if that's a bad move then I'm open to hearing what other arrangements are considered more preferable. I opened a blockchain wallet but haven't made use of it yet.