We conduct a comparative study of polarization properties of vertical-cavity surface-emitting lasers (VCSELs) from various sources, fabricated either by ion implantation or by the oxide-confinement method. An integrated test bench (iTB) for photonic devices is used to characterize the VCSELs. The ITB setup enabled simultaneous monitoring of the polarization state, transverse modes, wavelength spectrum, and optical power of the VCSELs under test. VCSELs commonly exhibit polarization noise, switching, and instability. The polarization behavior and related modal properties of various VCSELs are investigated based on aperture size, geometry, and fabrication processes. From the cw and pulsed pumping data, a general trend and inherent behavior is identified and polarization-related limitations are discussed.