Jesus Montero by quite a bit. Montero has a potential top 5 bat ceiling wise in the majors if he reaches that potential. At 19 he literally made older players in A/AA look inferior. A lot of prospect pundits are claiming he has Miguel Cabrera type talent but only question with him at this point is his questionable defense behind the plate. Given all that though you can't downgrade a bat like that no matter what position he plays because its just that special. This time next year your going to see Montero hype much like Heyward this year and I think he has a better bat then Heyward. Scouts put an 80 on the 20-80 power scale just with his bat alone(Michael Stanton was 80 as well for reference), prospects at that age with plate discipline, contact ability and power dont come along very often.
Chapman is a high risk high reward player but even his ceiling is not as high as Montero's and Montero has less risk then Chapman to reach that potential.
Finaly always take the superior bat over a superior arm. They contribute every day, and are less a risk for injury.