For the analysis of in vitro data I am using GraphPad software and utilizing various equation (logarithms) to fit data. How can I know that which equation should be used and it is correct ?
You can use F values as well as other statistics like adjusted r squared, AIC, and so on. The higher the F value and lower the p value, the better the model :)
Analysis of variance (ANOVA) is an F-test. For each model ANOVA should be performed. Criteria like AIC, BIC, SIC, usually accompany ANOVA results. The smaller each of these criteria the better the model.