Keeping in view latest developments in ardupilot viz a viz PX4, which stack provides mature, consistent, and feature-enriched platform in context of Copter only .
Simple answer : BOTH are mature , consistent , and feature-enriched platform!
Perhaps, but everyone knows that all the cool kids hang out here.
I think @khancyr gave a very politically correct but not very helpful answer
Realistically, you’ll struggle to find an objective opinion.
I’d suggest that you try both, get as far as you can by yourself, and when you get stuck, ask for help.
Then make a decision.