Jon always. Richie had a great voice as well, and perfect for backing and even singing lead on some styles but I think he never really learned how to properly sing lead vocals. He tends to over sing while beginning a line and then the strength he uses at the start by the end of that same line it's just gone. Lack of confidence could be part of it but I also think that he really lacks control and technique.

Edited to add that Jon's recent lack of strength in his voice is also something that should be noted, but at least he knows his limitations and holds himself back in order to get through a show, something Richie has yet to learn how to do. And in all honesty, I don't know which is worse....