Godot is yours to control. You, and others, can change the engine and share those changes.

Someone else controls what your copy of Unity does, and they want to get paid. They can alter the deal at any time. Spend year(s) investing while praying they do not alter the deal any further.

There are other considerations one can discuss (what do you want to make, user prior coding experince, what jobs want these days) but if you value your software freedom it's an easy question answered by looking at the software license. MIT > Proprietary.