I would pick the Divine Mercy Chaplet. As someone who prays in my own words as well as with written prayers, I have to say that, when I pray those that are written, my prayers tend to be less selfish. I’ve prayed the rosary, and love the scriptural rosary as a meditation tool, but I get much more out of the divine mercy—it is also easier for me to pray on the way to work, which I do every weekday. But then, I am hardly a typical protestant, since I hope, with God’s mercy, to eventually become Catholic–the only thing holding me back is my husband, who is hostile to the Faith (read that staunch non-denominational protestant–he won’t even join the United Methodist church that we have been attending for the last 3 years!)
Please pray for him.