i heard that a tear drop shap is the most aerodynamic shape possible or the best is this true? If this isn't true what is since i need to make a fast ROV? Also since i need to have a propeller to propel it should it be on the front or back to produce the most thrust and the best hydrodynamcics?
Best aerodynamic shape depends mainly on the application i.e. the desired speed at which it should work, interact with the air.
If you have heard, asymmetrical wings and snout nose are helpful in case of supersonic flights; since you want to minimise drag which is a killer at those speeds, while normal wings and pointed nose is better in subsonic flight. [see here]
Even the placement of propeller is dependent on the application. Submarines generally have propellers in the rear, while airplanes have it in front. I'm not an expert in this but they might be der for a reason.