Google, and Microsoft are popular providers of cloud services, offering equivalent features such as email, contacts (address book), calendars (diary), notes, file storage, and much more.
iCloud, being an Apple product, integrates closely with Apple devices and apps. As a result, iCloud is very easy to setup and use.
To use Google’s or Microsoft’s equivalent products on an Apple device will require just a little more effort to have them working smoothly.
As a rule, software and hardware developed ‘under one roof’ will be easier to set up, complementing and integrating seamlessly with other features. This is why Apple devices, and iCloud go hand in hand, and work so well together.
However, Google and Microsoft make excellent products that are hard to avoid. So it’s likely you’ll end up using them all.
There are numerous alternatives out there, but for most of us, Apple, Microsoft and Google are the best options in terms of the features we need to use, ease of use, cost, and support.