Outfield prospect Wil Myers, reportedly, is the trade chip the Royals are dangling.
If the Royals choose to trade Myers for a starter, Shields should be their man.
Lester has had a solid career, but he's coming off his worst campaign as a full-time starter. The veteran posted a 4.82 ERA and 1.38 WHIP, while going 9-14 last season.
Shields, on the other hand, is coming off his second-straight productive season, going 15-10 in 2012, while posting a 3.52 ERA and 1.17 WHIP with 223 strikeouts in 227.2 innings. That included a 2.81 ERA and 0.89 WHIP after the All-Star break. He pitched two shutouts during the season.
Of course, there is the sentiment in Kansas City that the Royals shouldn't trade Myers at all, given he batted .314 with 37 home runs and 109 RBI in the minors last season.
Also, Lester and Shields would be free agents after two seasons, so it's possible they could split in a couple of years.
On the other hand, you only have to look at the Royals' pitching in 2012 to know that a front-line starter is desperately needed. The Royals' starters posted a combined ERA of 5.01, 11th in the American League. Luis Mendoza had the best ERA among Royals starters with at least 16 starts in Kansas City, and his ERA was 4.23.
Especially in the American League where you have a designated hitter, it's important to have a strong starting rotation. The Royals could potentially build something with Shields and make Kansas City a place free agents want to go, even if Shields decides to leave down the line.
Myers is a very promising prospect, but pitching is more important, and Kansas City cannot survive with the starting rotation it has right now.