Have a look at this article. : https://www.dragonspears.com/blog/azure-container-orchestration-101-azure-web-apps-vs-aci-vs-aks

If you are new to the cloud native world and all the goodies that comes with it, have a look at the landscape https://landscape.cncf.io

Your best bet is to start small, focus on making your microservices small, consistent, and easily deployable in the cloud using ACI/WebAppContainer.

The more microservices you will deploy, the more requirements you will have. You will reach a certain level of maturity with your current deployment mechanisms and once you will need to push to limit a bit further, that's when you might want to look at migrating to AKS (Kubernetes). While Kubernetes might sound an ideal choice to jump straight ahead, I would say it depends on your wiliness to learn the ropes from the beginning.

With AKS you will be more in control, but with control, comes responsibility as well as time to dedicate and people to train to ensure that this control is properly managed.

With either of the two non-kuberentes solution, you will have less control but more ease when it comes to the whole management of the Infrastructure, with some limitations when it comes to complexities in the deployments and scheduling.

In my experience, you will hit the ground running with an App Service Plan running Web Apps for Containers. The resource model is simpler and is geared towards rapidly getting containers running. Web Apps for Containers is positioned in the market as PaaS (Platform as a Service).

Azure Kubernetes Service is a more flexible service that can accommodate nearly any configuration you can imagine. With that flexibility comes and overhead in terms of getting everything set up properly. In my mind AKS is closer to IaaS (Infrastructure as a Service) - Microsoft provides integration with Azure resources, but much of work to get an environment stood up and available lands on the user. Please see this link about support for clusters to get an idea of what you take on when using AKS as a compute resource: https://docs.microsoft.com/en-us/azure/aks/support-policies

Nothing stops you from starting with an App Service Plan and migrating to AKS later.

Which one is appropriate for you is going to depend a lot on your architecture, expected load, growth and any other requirements you may have. If you want to update your question with some details of that nature, myself or someone else might be able to point out some relevant constraints.