Least favorite to recieve- irimi nage. Sensei just changed how he wanted the ukemi for this technique...and it's insanely difficult (or maybe I just need serious work on my ukemi
I've also always had problems doing irimi nage (ura) because it was hard to get a good feeling of blending. (my ashi sabaki always seemed just a bit off)
favorite to perform- nikkyo. I originally hated nikkyo because I couldn't get it to work on anyone. So I spent hours with every yudansha I could find working with it and tweaking it. It works great now, so I love using it. I still play with it though. Somehow I don't think I'll be satisfied untill I can snap wrists with a twitch.