Endogenous versus exogenous QE monetary policy

There is growing discussion on differences in quantitative easing monetary policy. On the one hand, there is the activist exogenous monetary policy followed by the Bank of England and Fed through explicit purchase of financial assets in order to control rates. The purchase of mortgages or Treasury debt increases the central bank balance sheet. The purchase of specific securities is expected to lower rates directly. The central bank decides on the when and how much not the market.

On the other hand, endogenous quantitative easing has been followed by the ECB. In this case, the central bank sets a rate of interest but makes funds available to all that want them. The ECB balances has also exploded but it is based on the demand for funds by banks. The endogenous approach is solely based on market driven demand. Perhaps this is easier for a country that has more developed bank system but there has been less aggressive reaction to the endogenous approach than the activist approach.

Which is better? My guess is that the endogenous approach will be easier to reverse and control. The exogenous approach will require an active transaction of selling bonds by the central bank. The impact from their purchases could be offset by the future sale. The endogenous approach is a matter of banks making the decision of what they need from the central bank at its stated price. The bank doe snot have to do anything but change the price of money to change the balance sheet and demand.