I'm about to embark on a large project based around mobile web apps. I am going to create a mobile web app that will have multiple screens, a search system and a few other features.
I need to establish a primary framework for this application. It seems I have two options; multiple separate HTML pages, or alternatively, use AJAX to download the contents and move divs in and out of the viewport.
I don't have to worry about SEO. I'm primarily looking for good performance. I understand Stack Overflow is a site about questions and answers and this does somewhat involve opinion, but I feel that based on my criteria there should be a solid answer to this question.
I'd highly appreciate it if somebody could share what they think the best option would be for me on this project.
What I believe you're referring to by using AJAX to download the contents is commonly known as a single-page web app. These generally involve rendering data using templates on the client side and sending and receiving the data via AJAX.
Of these, Knockout is probably the easiest to learn (seriously, the tutorial is brilliant), but the lack of routing lets it down somewhat. I tend to use Backbone for this type of thing myself, although if I were starting over I would probably go for Angular as it's made by Google and seems to have more momentum. But try a few tutorials and see which one works best for you!
All of these offer a lot of very handy functionality for your use case, as they enable you to load data via AJAX and render it on the client side quite easily. There is a learning curve for all of them, but they result in a much more maintainable and testable client-side application. Believe me, I have tried to build such an application with just jQuery, and I would recommend you avoid it as it gets very painful, very quickly!
Your mileage may vary, but by and large a single-page web app like this should perform better than a more traditional web page because once the application has loaded, all the communication with the server is just sending and receiving JSON. It will also likely be simpler as you can use a lightweight REST framework like Slim, Sinatra, Express or Flask on the server side, and just serve up the static content on the home page, then do everything else via AJAX.