Selecting one cloud from many needs of each individual customer and the workloads they are running. all three abouve provide same features in compute, storage and networking. so it is very difficult to select one of them.
But AWS is the oldest player in this is provide amazing service to it's customer with large number of options in instance selection and additional services like CDN, Simple Storage (S3), Elastic Block Storage (EBS), Elastic File System (EFS).
Azure has benefit where Microsoft already has a strong footing within an organisation and it is links well with key Microsoft's systems like Windows Server, System Center and Active Directory
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AWS its free for first year after that you will get around $2 Month charge for basic website.
Great Cloud Services. :)