This study examines the relative effect of capital structure theories and the determinants to establish best understanding of the most appropriate theory to explain debt vs. equity hypothesis and the behavior of firms. The theories provide theoretical basis to compare with empirical findings of quantitative analysis. This study covers the period from the period 2001 to 2010 of listed companies of Karachi Stock Exchange, Pakistan. It is obvious that determinants of capital structure affect the choice of debt vs. equity in emerging and transitional economies. A number of econometric models from OLS to EBA are being used to identify the empirical evidences for this perspective. The results reveal that seven variables: investment growth opportunity (IGO), agency cost (AC), liquidity (CR), financial flexibility (FF), free cash flows (FCF), tax effect (DP) and interest rate (IR) have robust - signaling relationship and highly sensitive to debt vs. equity. This study explains the financial signaling and asymmetry of information risk due to debt vs. equity decisions. For the whole sample period, the study found evidence of financial signaling and information asymmetries of risk due to Debt vs. Equity decisions. There is a significant effect of the systematic risk (β), should also report about the persistence of negative effect during the sample period. There is a significant effect of the interest rate (IR). The empirical results report about the persistence of interest rate (IR) negative effect during the sample period. It is observed and resulted that increase in debt vs. equity negatively associated with the value of the firm. This proved inverse relationship among debt vs. equity and firm value variables. This showed inconsistency of prior findings as Modigliani and Miller (1958) theory that the market value is irrelevant to financial policy. The results presented that corporate corporate governance (CG) has significant effect on firm performance (FP) under transaction cost economics theory and good management theory. It is obvious from the results that corporate governance (CG) has significant effect on the firm value. In addition, it is also shown that corporate governance (CG) does have mediating and moderating effect in between the corporate financial structure (CFS) and firm value. The negative relationship shows an agency problem. Therefore, the investors do not have the equal information of the particular firm as the manager holds. Furthermore, the financial signaling and asymmetries of information hypothesis reflected that choice of debt or equity must have influence the behavior of the investor due to information asymmetries, it is seen negative and increase threaten of bankruptcy and financial distress. It is found that product and asset specificity diversification have a significant relationship with capital structure for best alignment of cost with trade off signaling and asymmetric risk. However, Extreme Bound Analysis (EBA) an econometric technique is used to analyze the variables and investigates the significant empirical findings. The empirical findings of the study have implications for risk management appropriately to reflect the effect on financial decisions in emerging and transitional economies.