Shawn IMO was in his prime in 2005 - 2007, he cut the best promos of his career especially against Hogan, in ring he was always stellar however. Jericho was at his best during the honest man gimmick in 2008-2009. I'll compare these two the best I can.
Shawn was the better seller, however Jericho understood psychology a lot better. Jericho had the better moveset IMO, Shawn was more flash but Jericho made heel working an art form that very few have matched.
Jericho still cut stronger promos during this time than anyone else for at least 4 years IMO. He was that good, he made me hate him and still does to this day especially how he stripped everything which made him enjoyable in the Y2J gimmick. I was never overly impressed with Shawn on the mic, however he was very good during this time.
My answer is Jericho, in ring it was very close with Chris just edging it based upon my personal preference, the promos were Jericho's by a larger margin but still very close.