Since we teach a balanced practice this is a very difficult question to answer. Because one single reflection at one single time has given me great benefit, but at another time, depending on what is needed, a different reflection has given me great benefit. Death reflection has been very beneficial in my life but I wouldn't want to be reflecting on death all the time. Reflecting on the Buddha has been a very beneficial reflection for me. I don't think I can limit myself to one reflection, because I have seen so many benefits from all of them. And we do teach a balanced practice. Compassion/Lovingkindness is a very beneficial reflection. So I guess you say, reflection on Dukkha helps to bring forth wisdom and compassion, and I guess if you could expand that, you could also include death in that and impermanence and a lot of other things.