Coinbase is probably the easiest one to use, but inputs.io is really good for security. I've never seen a website with more security than theirs. I only heard about Bitcoins recently so I don't have much to tell about past experiences, but making sure your wallet is secure is probably the biggest priority. Other people are saying blockchain.info is better for security than inputs.io, so I'd check them out, but to have more security than that is ridiculous.