My opinion, I like 7zip way more than WinRAR. For one thing, it is free. Second, it is lightweight and UI is exactly how it needs to be, simple. Third, it can be used as an alternative to Windows Explorer, you basically get a full-blown explorer while still being able to archive/de-archive everything. When I was building WinPEs, 7zip was what I used as explorer alternate, after trying many of them, and they sucked in the PE.
WinRAR 7.xx cannot create RAR4 archives anymore. Keep a copy of 6.24 around if you depend on it. Only creation (and updating) is affected, listing and extracting still works.
Nothing wrong with RAR5 itself, it's just that sometimes I need to send files to non-tech savvy people and they often have outdated software and whatever program they use tells them that the archive is corrupt..