CDisplay is the best program, but it's pretty out of date and you will have problems with specific zip-files, newer compressions (won't read .7z, etc.), and Mac-zips (dunno wtf that is about). It will also be slow if you try to quickly skim through a big file (50+ megs) on an older computer.
CDisplayEx tries to be CDisplay, but fails on all important things: Like, it won't let you control the page with your mouse. Pressing space won't scroll the page, it'll just jump the next one, you need to double-click the page to go to next page, you have to click and drag to scroll the image with your mouse no mode à la Japonais, etc. Useability failure. But, it'll read all the archives CDisplay won't, and handles big ones much more gracefully - great for when you want to fap to a cg-archive.
I use CDisplay, with CDisplayEx as a backup.