making a secure bitcoin wallet which is always offline and stays that way is not really hard, and i am talking from 2 years of experience with having only one bitcoin wallet on an offline linux system.
That means u dont use your bitcoin. For those who use bitcoin regularly, needs to wallet... one online and one offline.
Like the bitfinex's cases, I don't think a lot of their member are online at the time bitfinex are gonna get a hacked by someone. online or offline need more researching about the wallet of bitcoin have you used it. but if using the offline wallet I think that is always secure in your wallet online or offline.
Bitfinex is not a wallet. It is an exchange site. And leaving your coins on the exchange sites is not a good practice. Those people who treats their bitfinex account as wallet should have learned their lessons by now. You need an online wallet so you can spend your bitcoins easily, which is good for bitcoin economy. Most of your bitcoin should be in your cold wallet.