I struggle with just about everything, depending on the story and the situation. Sometimes action scenes are easy, sometimes they make me want to tear my hair out. Sometimes the dialogue just flows and sometimes it's like pulling teeth. Sometimes I get the descriptions spot on and sometimes I'm like, "Uh, what?" The one thing I really, consistently struggle with is romantic and shippy stuff. I have several ships that I like, but writing realistic romantic stuff (especially dialogue) always seems to be beyond me.