Hi, check out this thread → Is the Flight Model of the MSFS 2020 realistic or do we need a completly rewrite?
Hope it answers your questions. I own both sims, and especially now, knowing that X-Plane will undergo some next-gen treatment, certainly won’ t abandon it. MSFS has a lot of potential of getting even better, so I will definitely stick with it too, for now mainly for VFR flying with Piper Arrow/Turbo Arrow from Just Flight.
Regarding realistic flight model: for me, it’s not only the aerodynamics of flight, its also a realistic behavior of the engine which prompts you, as a virtual pilot, to abide by certain limitations. I.e - not to overboost turbocharged piston engines, unless you want them to overheat and eventually fail midflight, etc. Also - a realistic behavior of turboprop engines, good propeller slipstream effect simulation (or as its more commonly called - a propwash) and similar stuff.
Because MSFS is only a year old, there still aren’t too much aircraft models which support this complex behavior, but from what I can see and feel - they are definitely coming. You will see models in which even the movement of hydraulic fluid to the control surfaces is precisely calculated. You will see models which will bring realistic engine behavior. And so on, and so forth. X-Plane, being more mature, already has some really amazing models, such as the REP expansion for C172, Airfoillabs King Air 350 and some others, of course.
Current version of X-Plane is lacking in ground textures, atmospherics and clouds (I am talking about vanilla version, without installing packages which improve the experience). So maybe, you should wait a little bit until more is known regarding the next-gen version of X-Plane, and then decide whether to wait, or purchase the current edition (11.55).
Good luck and happy flying 