What is the best image file format to convert past images and "standardize"?

I have a huge repository of .png, .tiff, .jpeg and other image file formats.

My requirement is to

1. 
   

   Convert them to a single file format without significant image quality loss when viewed normally (images are not zoomed)

   
   


2. 
   

   Images are mainly photographs, some have large text fonts.

   
   


3. 
   

   Images must be all-browser compatible

   
   

Disk Space is not an issue