I don't know if Canon lenses are better or worse than others -- until my purchase of a 5d, since replaced with a 5d2, and a 24-105 I used Leica and Hasselblad lenses with the newest one having been assembled in the mid-70's and continue to be happy to use them when shooting film or perhaps digitally if I ever get to buy a M9. I am sure that newer Leica lenses are 'better' but one simply uses what one has.
I did 'test' my Canon 24-105 (at 24 and 40 focal lengths) against my Voigtlander 20 and 40 lenses. As I noted in an earlier thread the Voigtlander did better or at least as well as the 24-105 when mounted on a tripod and using LiveView.
I also tested all lenses for focus accuracy via the finder. My 24-105 requires a +5 AF Microadjustment; the VC 40 requires and +15 adjustment, and the 20 requires none.
Sergio, you may need to microadjust your lenses for your new body. It is not particularly difficult to do -- elsewhere on this site you will find a review of LensAlign, a system to accurately adjust lenses -- I made my own similar setup that seems to have given me the necessary adjustment. Once you microadjust your lenses you may find that they work much better for you.
Given the complexities of camera bodies and lenses with AF detection sensor locations, metering locations, motors, and who knows what else, it is not surprising that tin spite of tight tolerances some final adjustments need to be done for each and every combination of camera and lens. This is nothing new, since the beginning Hasselblad films magazines and inserts had to be fit for each other and are not really interchangeable, no two light meters ever matches each other exactly, I am sure that other examples abound.
Jean-Michel