7Zip is a good solution not only for occasional compression but also for simple backup or backup automated with scripts.
The normal usage with the flag “a” can be hugely overtaken in speed using this command
7z u -uq0 -mx9 "backup.7z" "sourcedir"
This command add/delete from the 7z archive only the modified files. The difference in speed can be amazing: e.g. on 10000 files with only few dozens of files changed, the difference could be few second against 1 hour using the “a” flag.