I have been reading about flight controllers on the Internet and trying to find out the best one. Unfortunately, the Revolution and Open Pilot do not seem to be recommended. So, I am wondering, what is the advantage of Open Pilot? Should I consider switching to a different controller and software? I amk just fishing for opinions here.
Depends what you want to do. You want race or do some autonomous flights ? It seems BetaFlight has more forgiving single loop PID controller, LibrePilot has dual loop PID controller and proper Autotune, which gives perfect PID, so that's I guess a tie. BetaFlight has always stabilized when armed (if you want to do diving and use that feature), LP has that broken in release but fixed in "next" branch if you compile yourself.
Also "next" branch contains more FC hardware supported. BetaFlight does not offer autonomous capabilities, its purely racing stack, LP has many interesting autonomous flight modes.
LP has multiple banks with configs which you can change in flight, no other software does.
I think both BetaFlight and LibrePilot can be flashed onto Revolution board, and I advise you not to listen to people who can often blame firmware for lack of their own knowledge, or there are people who complain about things that are their own fault but they like to blame others. I just can't imagine using different firmware than LP, you hate it or love it. Just try both yourself, that's best, perhaps give feedback to devs if something is missing.
When it comes to hardware F0, F1, F3, F4, F7. Well these are STM32 numbers.
F0 is Cortex M0 core
F1 is Cortex M3 core and little memory
F4 is Cortex M4F core with lots of memory
F3 is Cortex M4F with less memory
F7 is Cortex M7 with caches and lots of memory
there are differences between these MCU, like cache on F7 which is not used, bus matrix how internal peripherals are connected and how you can use DMA, technicals details, but currently we are not using 50% of F4 resources. One could oversample gyro on F4 and use CPU 100% and be stupid, but that would not give any measurable increase in flight performance. F3 core is an interesting MCU as it has built-in inverter on UART and could potentially do FrSky telemetry both ways.
I would suggest Omnibus F3 or F4 flight controller with integrated OSD for racing. LibrePilot will support that soon, its not merged yet but flies very well and can be compiled from dev branch (there is thread on forum how, and maybe someone posted binaries).
If you want to do autonomous flights, I suggest Revolution board or Sparky2.