The Kansas City Royals have discussed outfield prospect Wil Myers in trades for Tampa Bay Rays right-hander James Shields and Boston Red Sox lefty Jon Lester, according to Bob Dutton of the Kansas City Star.

Great idea. But who says Shields and Lester are equal?

True, their contracts are similar — Lester, 28, is owed $24.625 million through 2014, while Shields, 30, is owed $21 million. But Shields was the better pitcher last season, and has been an absolute beast for the past two years.

Lester, meanwhile, is coming off a career-high 4.82 ERA after four straight sub-3.50 seasons. His average fastball velocity of 92 mph in 2012 was the lowest it has been since ‘08, according to PitchFx data on Fangraphs.com. His cutter also declined in effectiveness, and in general, he was hit harder than before.

Some of Lester’s struggles might have resulted from poor luck — his .318 opponents’ batting average on balls in play was the fifth-highest in the AL, and his fielding-independent pitching mark was nearly as good as that of Rangers lefty Matt Harrison, who finished with a 3.29 ERA.

The Royals, if they acquired Lester, would count on a bounce-back season — the same type of season the Red Sox surely anticipate, particularly now that Lester is reuniting with his former pitching coach, new Boston manager John Farrell.

Shields, on the other hand, seems to be peaking.

His 477 innings the past two seasons rank second in the majors only to Justin Verlander, and his 3.15 ERA during that time rank fifth in the AL among pitchers with 60 or more starts. His stuff, if anything seems, to be getting better. His average fastball velocity of 92 mph last season was the highest of his career.

In baseball as in life, beauty is in the eye of the beholder. Perhaps the Royals actually see Lester and Shields as similar. Perhaps they would seek to expand the deals to compensate for any perceived difference in value.

True, Myers could develop into a star. But either Lester or Shields would amount to a major two-year upgrade for the Royals, giving the team a legitimate ace in front of right-handers Ervin Santana and Jeremy Guthrie in ‘12.

The question, then, is not only whether the Royals will pull the trigger, but also which target they prefer.

— Ken Rosenthal