I would choose 7zip because:
File size : The size of a RAR or ZIP archive, as well as the size of any single file within a RAR archive, is limited to 8,589,934,591 GB. The
minimum size of a RAR file is 20 bytes
7zip - Supporting files with sizes up to 16000000000 GB
Compression algorithms - WinRar has proprietary. 7zip uses LZMA derivatives, Bzip. Deflate, etc.
7Zip is slightly better for data compression. 7zip,winrar,zip,arc have poor performance with audio/video due to lossless compression as compared to aac,ogg,mpeg,etc.
7zip also has a theme manager
7-Zip Theme Manager similar to rarlab themes(which I absolutely like )