Answer:
The best system : Coordinate system at the launch point 
Step-by-step explanation:
 This is a problem of analysis, the objective is to facilitate the calculations, let's see ballast possibilities 
- Ground coordinate system 
In this case the displacements are all positive, even though there is a song that is the initial displacement (xo, I) that we must add to all the equations, 
Vertical speeds are positive in the first part of the trajectory and negative after the maximum point 
It may be useful in some cases, but it is not the ideal system for the equations 
- Coordinate system at the launch point 
In this system all displacements are positive, the initial position is zero, which simplifies the equations a bit 
The vertical speed is positive in the first pate of the movement 
This is the ideal system since it meets the criteria of the greatest number of positive variables and is the one that most simplifies the equations 
this is the best selection
- Coordinate system at the highest point of the trajectory 
In this case all X and Y displacements are negative, the velocities on the Y axis are positive before origin and negative after origin, 
This system does not meet the criteria of the greatest number of positive variables, so they would be bad choice