Well, this is a very broad question, since horses vary so much and are so individual regarding their training, temperament, and level of experience.
To answer your general question very generally, trained horses are easier to ride.
To answer your question specifically, it would have to be narrowed down to two specific horses, one trained, one green, and determine which is easier to ride. Some trained horses have formed bad habits, or require more control in certain areas. Some green horses are easy just because they have good temperaments....so it is kind of too general to lump all green horses in one group and all trained horses in another group.