Ok i dont play with leaders so i cant really advise you on them...but why you would want to play second is to work out a better strategy
and then theres the poison abiltity Poison X, Min Y
If your character wins the round, at the end of each of the following turn your opponent will lose X life point(s) if he has more than Y life point(s). If your opponent has Y or less life point(s), the poison effect is not triggered.
Very strong in the case of Nina (U).