What ever you do and how ever you store your bitcoins they will end up in a private key, one of the most convenient methods to store bitcoins for me of course after having a core wallet on a separate computer is generating addresses offline using bitaddress.org then saving addresses with their keys.
Another option which is convenient as well is visiting directory.io and entering a random page like: directory.io/30866184577
and picking 10 addresses with their keys and saving them in a text file.
Even I cringe at this... I just CAN't for the LIFE of me allow someone else to hash a BTC privkey for me and serve it through HTTP... no, just no, I won't do it.
You want ULTIMATE security, you use a paper wallet. You do that by making your OWN offline keys using Vanitygen on a PC with no internet connected. Put the keys on paper, in triplicate, store, and just send all your BTC to that address.
Then when you are ready to start using it, all you have to do is import that privkey into ANY wallet and the coins will be there.
Second time I have posted this here... there is no safer way... not even hardware wallets, laptops, hard drives, USB... none of it. All have failure points. A paper wallet's only failure point is your failure to be secure about storing them.