I do not know anything about GCP, but between AWS and Azure, go with Azure if you are at all new to this space (or if you're just looking to get something up and running quickly to prove a concept).

AWS takes the approach of giving you the building blocks which you then must assemble yourself. Azure gives you a silky-smooth GUI (ML Studio) with which you can have a model up and running in literally minutes. Of course you can also go lower-level in Azure if you want.