I'd add to John's advice something I've always looked at (almost first) when looking at these kinds of tech decisions:
How easy is it to get off that platform?
While privacy, security, redundancy, policy controls, audit abilities, & general management aspects are important, if you can't easily migrate to a new platform in 5 to 7 years, then you shouldn't use it because you'll be locked in or involved in a painful migration.
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I'd add to John's advice something I've always looked at (almost first) when looking at these kinds of tech decisions: How easy is it to get off that platform? While privacy, security, redundancy, policy controls, audit abilities, & general management aspects are important, if you can't easily migrate to a new platform in 5 to 7 years, then you shouldn't use it because you'll be locked in or involved in a painful migration.