Three different GaAs Monolithic Transimpedance Amplifier topologies for low noise and high speed optical communication systems are compared. The first one consists of a simple cascode stage enhanced in terms of bandwidth and noise. The second one is also based in a cascode stage followed by a differential amplifier in order to increase the transimpedance gain-bandwidth product. The third one was designed with that same scope in one hand and in the other to obtain a very low power consumption; it consists of a three stage inverter amplifier with reactive feedback loop. Measurements show that excellent results have been obtained for the first topology; for the second one a remarkable improvement of the bandwidth has been obtained; finally, for the third one, high gain and extremely low power consumption have been obtained. In all cases the equivalent noise current is low enough to achieve a sensitivity of the receiver between -28 and -33 dBm.