This post is completely consumed from Microsoft Azure site . . . But i found this information really useful and would like to archive on my blog as well.
Azure offers several ways to host your web applications, such as Azure Web Sites, Cloud Services, and Virtual Machines. After looking at these various options, you might be unsure which one best fits your needs, or you might be unclear about concepts such as IaaS vs PaaS. This article helps you understand your options and helps you make the right choice for your web scenario. Although all three options allow you to run highly scalable web applications in Azure, there are differences which can help guide your decision.
In many situations, Azure Web Sites is the best option. It provides simple and flexible options for deployment and management, and it is capable of hosting high-volume web sites. You can quickly create a new web site with popular software, such as WordPress, from the Web Application Gallery, or you can move an existing web site to Azure Web Sites. Using the Azure WebJobs SDK (currently in preview) you can also add background job processing.You also have the option to host web applications on Azure Cloud Services or Azure Virtual Machines. These options are good choices when your web tier requires the additional level of control and customization that they provide; however, this increased control comes at a cost of increased complexity in application creation, management, and deployment. The following diagram illustrates the trade-offs among the three options.