Which of the following molecules has the maximum dipole moment?

In ${\mathrm{NH}}_3$, H is less electronegative than N. Hence, the direction of dipole moment of each N-H bond is towards N and create high net dipole moment.

In ${\mathrm{NF}}_3$, F is more electronegative than N, thus the dipole moment of each N-F bond is directed towards F atom which is opposite to that of lone pair, hence reduces the net dipole moment.