What does hardest mean? If done properly, they are all hard to do. There is a difference between discomfort and difficulty. For me, chins, cable and dumbbell rows are the most comfortable and all the bent over back exercises are the most uncomfortable.
Yes.
Easiest least uncomfortable for me.
Chins, pull downs, seated rows.
Hardest most uncomfortable,
Deadlifts, BB Rows, T Bar rows.
DB rows fit in the middle.