The best stub selection for the transmission line will be Shunt short.

- Introduction:
When designing a transmission line, it is often necessary to add stubs to the main transmission line in order to improve its performance or match its impedance to the load. These stubs can be either series or shunt connected to the main transmission line. In this case, the best stub selection is a shunt short.

- Impedance matching:
One of the primary reasons for using stubs is to match the impedance of the transmission line to the load. Impedance mismatch can lead to signal reflections and loss of power. By adding a stub, we can introduce additional reactance to cancel out the reactance of the main transmission line, resulting in a better impedance match.

- Series stub:
A series stub is connected in series with the main transmission line. It introduces a reactance that can cancel out the reactance of the main transmission line. However, a series stub can only cancel out the reactance at a single frequency, making it less flexible for impedance matching over a wide range of frequencies.

- Shunt stub:
A shunt stub is connected in parallel to the main transmission line. It introduces a reactance that can cancel out the reactance of the main transmission line. Unlike a series stub, a shunt stub can cancel out reactance over a wide range of frequencies, making it more versatile for impedance matching.

- Shunt short:
A shunt short is a type of shunt stub where the stub is short-circuited at the end. This means that the shunt stub acts as a short circuit to the main transmission line at the operating frequency. This is advantageous because a short circuit has an impedance of zero, effectively canceling out any reactance in the main transmission line. As a result, the shunt short provides a perfect impedance match between the transmission line and the load.

- Advantages of shunt short:
1. Provides a perfect impedance match between the transmission line and the load.
2. Can cancel out reactance over a wide range of frequencies, making it more versatile for impedance matching.
3. Does not introduce any additional losses in the transmission line.

- Conclusion:
In conclusion, the best stub selection for the transmission line is a shunt short. It provides a perfect impedance match, cancels out reactance over a wide range of frequencies, and does not introduce any additional losses.