This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
It's not possible to pick a "best", because they don't offer the same feature sets. Any such decision would be relative to your requirements. You may want to read up on the various types of cloud services, especially SaaS, PaaS and IaaS.