Definitely in cold storage as the bitcoin hard fork is coming up.

Don't wanna risk losing all your life savings of bitcoin because the exchange site or the wallet site you are storing your coins on doesn't give you the option of getting 2 coins from 2 blockchains.

The safest way is to get a hardware wallet, like trezor or ledger, and then store your bitcoins there.

And back up your seeds, of course.