The advent of highly sensitive interferometric arrays has rendered the detection of the redshifted 21-cm signal from early cosmic epochs possible. However, even the best data come mixed with bright foregrounds, effects of instrumental gain, and various modeling errors. These effects corrupt the data and make statistical detection difficult. This work presents a comparative analysis of a combination of these effects on the detectability of the 21cm signal for different telescopes. Simulations are performed using fiducial signal and foreground models, for different telescopes. The impact of two significant sources of error — instrumental gain and sky model — is analyzed for observations at 142 MHz (or z ~ 9). The effect of their presence on statistical detection of the cosmological signal will be discussed.