The paper presents a comparative study among several state estimation formulations, in the presence of GPS-synchronized phasor measurements. The presented approach is based on a hybrid state estimation formulation, which uses both traditional SCADA measurements as well as phasor measurements. Three different formulations are presented that use: (a) Cartesian representation of state and measurements, (b) Cartesian representation of state and measurements with the addition of pseudomeasurements, and (c) polar representation of state and measurements. A physically-based three-phase model of a power system is utilized. The three formulations are compared in terms of error and confidence level analysis, via a simple introductory example.