What contract type is good for a mobile app development project, fixed price or cost plus incentives?

Its a bit confusing.

When you develop a program, You are taking someone's time. If you know exactly what do you want. This means App specifications, diagram and functionality Then it is a fixed contract!

The same software can be delivered by Xman in30 hours and Yman in20 hours but the deliverable is the same product you want. so pay Fixed contract unless you are recruiting the developer to work for you and didnt mean to outsource the app to developing company.

Thank you!

cost plus incentive