There is consensus that the future evolution of the space debris environment in the LEO (Low Earth Orbit) regime is not stable and that active debris removal (ADR) is necessary to control the growth rate. First ADR mission designs are being intensively discussed and significant effort is put into the identification of suitable removal candidate objects. In this paper we analyze the effect of ADR on the long term evolution of the space debris environment in LEO in different scenarios using ESA's Debris Environment Long Term Analysis (DELTA) model (with variations on the implementation of the mitigation measures, on the traffic models and evolution, on the removal selection criteria and on the solar flux). For each of the scenarios we derive a list of candidates based on the objects involved in catastrophic collisions. A combined list is then created with the objects which appear repeatedly in the different scenarios. Finally, this list is used as input for ADR simulations and the effectiveness of the removal is evaluated in terms of number of objects reduced and number of collisions avoided.