The perfect course?
The fastest I ever ran was on an out-and-back course with a hairpin turn. I wasn't crazy about the turnaround, but it didn't seem to matter. I set a personal record, anyway.
Runners will tell you the perfect course is flat, with a very slight drop approaching the finish line; dirt surface, asphalt if necessary, but no concrete; a wide start area; few, if any turns (ha!); no bridges; no vehicles or pedestrians on the course; and the finish line very close to the start line.
As a race director, you can't always create such a course. If you have two events, e.g. 5k and 10k, it's even more difficult, especially if you want them to start and finish at the same place.
Decide your priorities for a course. Municipal requirements, topography, and geographic limitations may make the perfect course unattainable. Explain to your course certifier what you are trying to accomplish and trust that person's skill and judgement.
You may have to settle for something less than perfect. That is usually OK.