Select top 2 employees based on Grade and Alphabetical Order
About performance

As a forewords, I'm not sure you should be obsessed with performance as a beginner (actually I'm pretty sure you should not but surely others will disagree).

Consider reading : https://softwareengineering.stackexchange.com/questions/80084/is-premature-optimization-really-the-root-of-all-evil

With that said...

In the Employee class :

As said by coderodde, your compareTo can't be made faster.

In the EmployeePicker class :

PriorityQueue isn't made with performance in mind.
Seeing your code there is no point in using this class over a TreeSet and I'd really recommend using a TreeSet over anything else.

If you really are obsessed with performance, PriorityQueue may outperform a TreeSet when you have over 20_000 elements for your specific use case.

However, if you are really really obsessed with performance and you know all the employees as soon as the program starts (and then only have to retrieve some of them after that) then you should consider using an array that you sort once... it'll also be the most space-efficient solution of the three.

With less than a hundred elements, I'm pretty sure you can consider all solutions equals in performance.

Conclusion : IMO use TreeSet unless you have good reasons not to :)

About code format

You should make the fields of Employee private and final and create getters for them. When a method have multiple parameters, you should always follow the comma with a space (makes code more readable).

The indentation in compareTo is really confusing.