The two middos that I will always remember Rabbi Singer ztz"l for are Simchas haChaim and Ahavas Yisroel. Simchas haChaim - nobody had as much enthusiasm over everything like Rabbi Singer. There was nothing mundane about anything he did. Nobody had as much energy to dance on Simchas Torah, or to say a bracha under the chuppah, or even just to greet you. I lived pretty far away from Rabbi Singer's house but I would occasionally make the trek on a Shabbos afternoon to his 'garage' for some Torah. I remember one time I answered a question that Rav Singer posed. From then on, he greeted me like I was the gadol ha-dor. Now let me say right here, that I didn't become a baal teshuva until I was 26 years old. My learning skills were very limited. But he told me that I had such a good head on my shoulders and that I should be in yeshiva and I could be giving classes eventually. When the yeshiva opened on Passaic Avenue, I started attending one of the night sedarim. Rabbi Singer always made a point of walking over to where I was learning and telling my chevrusa or the rosh chabura how smart I was. Except for maybe my parents, he was my biggest advocate. What a wonderful person. At first, I wasn't sure how genuine it was. Maybe he's just kidding around with me; trying to pump me up to get me to make donations to the yeshiva. But he never asked me for a dime. And his excitement and his compliments were continuous over many, many years. There was never a time when he saw me that he didn't greet me the same way. Never! Even the last time I saw him, he was standing in the middle of the circle on Simchas Torah, and when he saw me he told me he couldn't believe he never got me to give a shiur at PTI.
I have heard it said by many people that Rabbi Singer's Ahavas Yisroel was so great because he loved every Jew regardless of where they were holding in their Yiddishkeit. I can't really speak to that but I can speak about the depth of his love for each Jew. He remembered everyone's name and their situation in life. He not only wanted every Jew in yeshiva, he wanted to know how he could motivate each Jew to have him want to be in yeshiva. Was it an encouraging word? Was it a kick in the pants? Maybe some food would help? Rabbi Singer was willing to do anything to get you into the yeshiva and then to get you to thrive in your learning once you were there.
I never had the privilege of meeting Reb Aharon or Reb Moshe, but I can only imagine how great they must have been if their talmid was Rabbi Singer ztz"l