Online wallet is the most efficient way now for storing bitcoin since bitcoin holders nowadays are preferred to do short trading rather than just wait for a year. I preferred online wallet too since my bitcoin is just small amount and I always buying on online merchant using bitcoin as mode of payment. Offline wallets sometime are too complicated especially for a computer that has a poor performance, Syncing of wallet takes time and too much electricity. At last, I love online wallet because i can access my bitcoin through my mobile phone anytime and everywhere that has an internet connection.