Which javascript minification library produces better results?

Between Yahoo! UI Compressor, Dean Edwards Packer and jsmin, which produces better results, both in terms of resulting footprint and fewer errors when obfuscating.

Better is a bit subjective here, since there are multiple factors to consider (even beyond those you list):

1. Compressed size doesn't tell the whole story, since an aggressive compressor can result in slower run-time performance due to the additional time needed to run unpacking code prior to browser interpretation.
   • Errors are easiest to avoid when you control the input code - judicious use of semicolons goes a long way. Run JSLint over your code, and fix any problems reported.
   • The style and size of the code itself will affect the results, of course.
   • And finally, it's worth keeping in mind that server-side gzip compression will always result in a smaller download than any code compression, although some code compression tools will combine with gzip more effectively.

My recommendation is to run the code you intend to compress through several compressors (an automated comparison tool such as CompressorRater helps...), and choose based on the results - remembering to test, profile and compare the actual page load times afterward.