I saw there're a lot of downloadable files were compressed in rar compression.
There're a lot of compression tools available, like winrar, winzip.
I think winzip have more nice user interface while winrar could compressed files more smaller than winzip.
any suggestions?

Whatever floats your boat... It really depends on the person which of the two suits him/her... but if you're compressing files with foreign characters like hangul or katakana, etc, winrar is better coz it can read these characters. Unlike winzip wherein you have to remove the foreign characters in order for it to compress the files...

Don't forget with WinRAR you can set passwords which you can't do with WinZip.. I think WinRAR is also compatible with more file types then WinZIP so I would say choose WinRAR but it's up to you..

I use WinRar. Used WinZip a long time ago and though it doesn't work as good compared to WinRar. WinRar to me is simple to use and fast. Also, WinRar says it's one of the few applications that can create Rar archives.