What is more important to a business, a good manager, or a good leader?

A good manager should be a good leader. If they are not a good manager then they are not really leading anyone.

You're confused; the leader is not the manager.
The leader or boss makes all the difference.

Yes, this should be only one person who is a good manager and a good leader. Rarely will you have both in a company as it is a waste of money/time. Unless it's a large corporation where a few lazy asses don't weigh in.