QLPreviewController VS UIWebView in terms of rendering efficiency and memory usage

Question

I am working on an iPad project that allows users to view local documents, ppts, pdfs, etc.

I have two options for displaying these files:

First, I can use UIWebView to display them;

Alternatively, I can use the QLPreviewController to display them.

From ActivityConsole, I find out that when I use UIWebView to display 8.6M PPT, my application process is as follows:

However, when I use QLPreviewController to display the same PPT, there will be two processes:

I think the quicklookd process is an auxiliary process launched by the QuickLook platform.

As I can see, overall memory usage is about the same, but using QLPreviewController can reduce the memory usage of my application (this is proven in the Tools). Therefore, I think that displaying a document can be smoother and faster using the QLPreviewController. However, when I test these two questions on iPad1, iOS 5.1.1, I find out that the profitability of QLPreviewController is lower than UIWebView. Scrolling ppt chokes even more in the QLPreviewController.

Can someone explain the main tool of the QLPreviewController rendering process? And which one is better to display documents?

Or is there a better approach to displaying documents other than the above statements?

Thanks for the help!