Measuring altitude from take off point

I am trying to develop custom altitude hold mode using px4 stack. I am trying to find current altitude parameter in px4 stack. I found one parameter in vehicle local position file . Is this the correct parameter that gives accurate current altitude?
I have noticed that there are three different filters, Position_estimator_inav , local_position_estimator and ekf2 , used to calculate altitude and we can select particular filter by changing the variable sys_mc_est.
I want to know to get a stable value of altitude which filter has to be used?