Zip or RAR?

Granted a rar file does better at compressing, has a free download but requires a purchase after 40 days.

Zip is native to windows now so it is readily available, plus winzip is also a free download but requires a purchase after 21 days.

But both will let you unzip things as long as you deal with their expired warnings. But zip requires people the think much less, rar still confuses some people.

RAR and don't look back... unless you are working with the great unwashed, then like you said zip is now native to win-blows.