I would be a little cautious with Coinbase. There was a recent post on HN[1] in which someone had a 5 figure transaction be approved on the site, but never received his funds. The slow response from Coinbase wasn't too encouraging, but the more troubling issue is that a large sum of money like that can just appear in the system without anyone noticing. It indicates that their level of accounting and auditing isn't up to the standards of even most brick and mortar businesses let alone a financial institution.

[1] - https://news.ycombinator.com/item?id=6929705