Which is better Amazon s3 or nginx server?

I am working on a web application built on java with Gwt and hosted on Tomcat Apache. We are saving our static images and content on Amazon s3 which we are using it as a CDN by activating Cloud Front. Now, The issue is that still our website is taking time to load and for processing which is not favorable for us. Till now, what i studied about speed and website optimization is by reducing the size of images,css,js etc. Through the study I came across nginx server which is used for optimization purpose. I have gone through the benefits of it, and tried it for amazon s3 also and still searching others.

MY PROBLEM:

My problem is basically that I want to know that which will be better for us staying on amazon s3 or moving to nginx server for optimization purpose.

In future the load on our website will be in thousands of multiple request. How should we manage what will be a wise decision to stay on amazon s3 or move on to nginx?