Both of these cloud service providers are excellent, and the differences between them is just getting smaller and smaller everyday. If you are choosing to learn or use any one of them I would suggest comparing the individual services that you wish to use, such as virtual machines, database offerings and so on. To determine which one is better, you should get a good understanding of the differences between the two and then make up your mind about them.
Time in market: AWS has been around for longer than Azure in the market. AWS was launched in 2006 and Azure was launched in 2010.
Market Share: Since AWS has been around for a longer period of time AWS has bigger market share.
Open Source: AWS has a better Collaboration with Open Source communities.
Hybrid Cloud: Azure a better Hybrid Cloud market than AWS.
If you are planning on learning AWS or Azure, as a beginner it would be better to start with an online course that teaches you the basics and also gives you hands on experience.
For Azure you can either take this end-to-end certification course which will teach you the basics of Azure, or if you are just a beginner and wish to get your feet wet you can watch this end-to-end Azure tutorial.
For AWS you can either take this end-to-end certification course which will teach you the basics of Azure, or if you are just a beginner and wish to get your feet wet you can watch this you can watch this end-to-end AWStutorial.
Back