|Much depends on what the word "suggestion" means to your manager. Looking at the history of your working relationship with him, are his suggestions friendly hints or are they friendly directives?|
Your best move is to meet with him to discuss the promotion. Although you can indicate that the employee he spot-lighted has some strengths, be sure to present specific data that unequivocally demonstrate that the employee you prefer is better suited for the new position. You should also have an idea of the kind of position that better suits the employee whom your manager prefers.
The fact is that you have continuous performance data on each of the employees in your department, while your manager has bits and pieces of information gathered over time. As a result, you need to fill in the blanks. Be certain that your discussion covers what is best for the company, the department, and the individuals involved. After all, is it fair to his favorite employee to promote her into a position for which she is not qualified?
If your manager still firmly suggests that you promote his choice, it is apparent that he has other reasons for pulling strings for this individual, while simultaneously turning you into a managerial puppet. In such a case, another firm suggestion is for you to keep your options open.