How can I achieve the best, standard ZIP compression?

I don't care how long it takes to compress, all I want to achieve is two things:

• The absolute best possible compression ratio


• Compatibility with standard readers, such as Windows and WinZip

So suggestions such as 7-zip won't be of much use, unless 7-zip is also slightly better at the standard ZIP compression (as opposed to using it's very good .7z format).

Ideally I'm looking for:

• A recommendation of a piece of software


• The particular settings for that software that enable the absolute best compression


• Something that's free

Remember, how long it takes to compress is not an issue!

One last thing - some files might be better compressed with different settings, like the "Word size" or "Dictionary size" - is there a tool that can analyse the files and choose the most appropriate compression ratio, or does WinZip, 7-zip etc. already do that?