It's a PMOS current source. their difference is their equivalent impedances. the diode connected load is simpler but it's small signal resistance is 1/gm (low impedance node) while for the one with a current mirror has a small signal resistance of ro (high impedance node). a higher impedance load gives a higher gain but needs a biasing circuit as shown. moreover, the diode connected load has a lower gain but is more linear because it's gain is dependent on the aspect ratio of the two transistors.