Beginner Flight Controller Recommendation for ArduPilot (Budget Option)

Hello everyone,

I saw that there are many flight controllers listed on the ArduPilot website. Which one would you recommend for a beginner like me, preferably a budget-friendly option?

I have already bought a FlyingRC 4in1 75A ESC.

My goal is to build a drone and later use it for my bachelor thesis.

Thank you very much in advance!

Best regards,
Wesam