I started using Coinbase and mycelium, I have around 10 BTC
Which one is the safest?
No one says you need to choose just one, each has their own benefits.
Personally I leave around 1 BTC in coinbase if I need to send BTC while I'm out and about because its so easy to access and send, I can also use the BTC stored in the account to sell quickly if BTC starts heading to the moon and I want a little more fiat.
The majority of my coins are then placed in cold storage paper wallets, with the remaining in local encrypted wallets (Armory).