Two Captains
I flew 32 years for a corporate operation that used the two captain "most of the time".
If they needed a fill in/contract pilot to cover a trip that's what they did, and we just naturally reverted to a captain/first officer operation.
My only problems with the operation came when they would bring on a new hire, who had no experience on the aircraft, put him/her through school, then, first trip on the line, assign them as captain, as if they had been flying the aircraft for years..
There was no opportunity for the new guy/gal to get a feel how we operated, and let he/her just come out of the box and just start doing things the way they had picked up from previous experiences, and then often looked sort of "limited" in operational expertise.
It just seemed logical to me that the new "captain" should spend some time under "supervision" until everyone was was comfortable with how things were working out. It happened numerous times.