i think coinbase because backed by trusted investors and used by millions of customers globally, Coinbase is one of the most popular and well-known brokers and trading platforms in the world. The Coinbase platform makes it easy to securely buy, use, store and trade digital currency. Users can purchase bitcoins, Ether and now Litecoin from Coinbase through a digital wallet available on Android & iPhone or through trading with other users on the companys Global Digital Asset Exchange (GDAX) subsidiary. GDAX currently operates in the US, Europe, UK, Canada, Australia, and Singapore. GDAX does not currently charge any transfer fees for moving funds between your Coinbase account and GDAX account. For now, the selection of tradable currencies will, however, depend on the country you live in. And of course I should mention FreeWallet. It is very convenient to use, rather fast and nothing have ever been stuck there, the longest transaction I had was 3.5 hours, but normal for ICO crypto, which I put out into BTC, most likely. And in freewallet you can sent BTC without commissions, although usually it is around $15, so this is a very nice bonus.