better winrar compression

I am making a weekly backup batch file for my work directories.
I am using robocopy to gather them all into a temp directory then using winrar command line to compress them and send them to my external hard drive. In the GUI for winrar there is a setting to select speed over quality. I believe the options are
Fastest
fast
normal
slow
best


Does anyone know of the command line option to make the compression 'best'?
Thanks,
-Adam

http://freebsdhowtos.com/67.html

Spoiler: -m5

Thanks
To bad best only saved me 1gb of space...

Does anyone know of the best compressor avaliable in command line for windows?

-Adam

winrar on m5 probably is the best, i have not benchmarked against others. How does tar.bz2 compare for file size?