The best strategy to improve the performance of the Visualforce page that loads slowly due to the large amount of data it displays is to use lazy loading to load the data on demand, instead of in the controller's constructor. Lazy loading is a technique that defers the loading of data until it is needed, which reduces the initial page load time and improves the user experience. The developer can use JavaScript and AJAX to implement lazy loading, such as using the apex:actionFunction or apex:remoteObjects tags. Using an apex:actionPoller in the page to load all of the data asynchronously will not improve the performance, as it will still load all of the data at once, but in a repeated manner. Using the transient keyword for the List variables used in the custom controller will prevent the variables from being saved in the view state, but it will not reduce the query time or the render time. Using JavaScript to move data processing to the browser instead of the controller will not improve the performance, as it will still transfer all of the data to the browser, which might cause memory issues or browser crashes. Reference: [Lazy Loading of Data in Visualforce Page], [Visualforce Developer Guide]