Which is better for improving work skills? Rotation between employees positions on periods,or maintaining on positions beside giving training courses?

It actually depends on the industry.

For an industry which is tech savvy, where technologies are getting updated frequently, and attrition is high, it is better to rotate employees by switching roles based on the requirement, it serves two purposes, the employee is getting additional skills for a new role, the employer gets the privelege to use the employee as a substitute in case of attrition.The shortcoming would be employee may not be able to work in the same role for a longer period of time to develop expertise.

On the other hand, it would not be so wise to rotate employees for a core industry, which concentrates on a specific set of products or services, it is better to let the employee learn and update himself for the current role, by doing so the employee is improving his core competence, and skills for doing the role more effectively, but its quite difficult to replace him after he has developed the core competence and expertise.

job rotation is a technique used by some employers to rotate their employees' assigned jobs throughout their employment, thus Along with the company providing the opportunities and training for job rotation, the employees who participate in job rotation learn more than the one job specification deemed to them, benefiting them in the long run in case of an open position on moving up in the company or a position opening up in another firm. Along with employees benefiting, companies benefit as well.

yeah rotation is important to get good output from the team members that will keep the run for the top always at the same time we have to keep them focus on mission nd vision of our company appreciation and gifts increases team members performance

It depends on the Organization Culture and Dynamics, also it depends on the organization plans for its employees development and retention.

Maintaining on positions for technical jobs. Positions like procurement need to be rotated from time to time.

No this is a practice which puts customers in a problem.

consistency,competence and visibility

Training Courses and Adding Resposiblities with appreciation 

Many of us could benefit from tweaking at least a few of our skills,in order to become more effective.we'll look at the skills you can develop in order to become more effective at work,and we'll reviews strategies and resource that you can use  to increase your effectiveness.

maintaining on positions beside giving training courses

Based on the field. If it is a vocational skill. OJT is the best enhancing method for skills. If it is management skills, rotation and shadowing would be the best.