The image quality is equally as good . Image sensor the same size and had the same generation . But the difference between the 600D and 60D are on a faster processor that speeds faster consecutive photos .
Another difference is the key for fast access , in addition there is an extra LCD on the camera also has a larger viewfinder .
Physical battery was too big so that it can be used for long shooting sessions . If weight is not an obstacle. Canon products do have advantages in this factor .