Chacin should never be put over Lilly in any major league rotation. Chacin is about as overrated as you can get in the majors.
He pitches up in the zone, gives up a lot of hits, walks a lot of batters and doesn't strike out many... all that does not = long-term success at the major league level. I honestly don't see Chacin as more than a #5 starter on a good team... MAYBE at best a #4 guy.
Most people immediately point to the W-L and spout off things like "he knows how to win". Umm that's nice but how often does his offense bail him out of his bad starts?? Shouldn't "knowing how to win" also mean actually pitching well and giving your team the best chance to win??
He had a nice year last year (very flukey IMO though) but unless he magically develops some better command of his pitches or develops a true out pitch, some of the casual Blue Jays fans are in for a big dissapointment with him in the long run.