Want to see more comparison between lenses for Canon.
The Digital Picture does a fantastic job with center, corner and mid-frame crops: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-... Highly recommended, their reviews are also fantastic.
Great resources. These are almost always qualitatively correct but it's hard to see the lens performances in real settings (out of paper) and to get an overall holistic view of the differences in "looks" . Both approaches have their merits.