Amazon Web Services

Strengths: AWS is widely viewed as the safe choice in public cloud because of its longtime market leadership, with appeal to customers looking for a broad range of capabilities.

"It is the provider not only chosen by customers that value innovation and are implementing digital business projects, but also preferred by customers that are migrating traditional data centers to cloud IaaS," said Gartner.

More than 2,000 consulting partners, offering managed and professional services, ease implementation, migration and management. AWS also enjoys the broadest ecosystem of ISVs.

Cautions: Expertise is needed for implementation of advanced features, according to the research firm. But Amazon's extensive training and certification programs, along with accreditation of managed services partners, helps customers find experienced consultancies.

"Customers should be aware that while it's easy to get started, optimal use  --  especially keeping up with new service innovations and best practices, and managing costs  --  may challenge even highly agile, expert IT organizations, including AWS partners," Gartner said.

While perceived as a cost leader, Amazon's granular pricing is complex, and it's not "eager to be the lowest-cost bidder in a competitive situation."