Which simulator is best suited to evaluate a new airframe and mixer?

I’m working on a project, where we are building a drone from scratch. We are gonna use a Pixhawk 4.

My current task is to create an airframe and mixer for that drone. Since I’m absolutely new to this, it will probably take a lot of tries for me to get it right. Therefore, I would like to be able to simulate the airframe and mixer before trying it on the actual drone. I saw that the px4 developer guide lists a lot of simulators to use with px4. However, I struggle to figure out which simulator I should use for this task. And I think trying out and reading about each and all of those simulators would take a very long time.

So my question is basically: Which of the simulators from the developer guide is most suited to evaluate a new airframe and mixer? Since each of the simulators has a list of vehicle types that are supported, this question also includes if it is easy to add new vehicle types to the simulator?

I didn’t find a way to edit my Question, but I would like to add something. Please notify me, if and how you can edit.

From the developer guide’s descriptions of the simulators I would assume, that “FlightGear” or “AirSim” can do what I am looking for as they are supposed to provide “physically” realistic simulations. As FlightGear seems to be focussed on simulating different weather conditions, I would further assume, that AirSim will be my way to. Can anyone share some experiences on those to simulators? Maybe even reagarding to my questions above?