Even though at best settings 7-Zip generally beats RAR5 (oddly rebranded as "RAR" format some time ago, while the old .rar format is now called RAR4 for no good reason) in sheer compression ratio, I do prefer WinRAR as my default tool.
I favor RAR's support of recovery record and volumes, the customizable self-extraction module and the settings depth for all features. 7-Zip is a bit too simple for my needs although I haven't explored it extensively. Surely the command line tool must be quite interesting but so is WinRAR's.
It helps that I won a WinRAR key a while ago when I wrote a review about it, but I can see why most users would just install 7-Zip for regular use.