How will you quantify best performing employee in terms of quality and quantity output?

It's very difficult to quantify "best performing employee".  For example, your "best performer" based on KPIs (Key Performance Indicators) may be so horrible to work with that they are the principal factor in having high staff turnover and consequently mediocre team performance.

Most roles involve interaction with other humans, and the results of that are always very difficult to quantify.

A thought experiment I sometimes used to do is imagine that you have to fire 3/4 of the team.  Who would you keep and why?

Points that must be taken into consideration for evaluation of the employee's performance are:

•  Assess its productivity
•  Analyze the progress realized
•  Communication with his colleagues
•  Self motivation
•  Versatility
•  Capacity of innovation
•  Compliance with safety instruction
•  Willing  to learn
•  Collabortion
•  Ability to react quickly
•  Individual performance
•  The rapidity of execution of tasks
•  Discipline
•  The obtained reslutats
•  Estimate the value added of the employee
•  The quality of work
•  Assessments of capabilities and apptitudes
•  Analyze the effectiveness
•  The absenteeism
•  Resolutions of quality problems encounted in the  production
•  Assess the performance
•  Assess the cost per activity of employee
•  Evaluate and appreciate its potential

Performance can be:

1. Exceptional
2. Superior to the job requirements
3. Fully corresponding to the job requirements
4. Acceptable that requires an improvement in one or more essential points
5. Inadequate and inferior to the job requirements

Target Settings:

 A natural step is to start setting performance targets to give everyone in the business a clear sense of what they should be aiming for.

Strategic visions can be difficult to communicate, but by breaking the top level objectives down into smaller concrete targets you'll make it easier to manage the process of delivering them. In this way, targets form a crucial link between strategy and day-to-day operations.