Most residential kitchens require at least one seam in their countertops. Although a good seam should be inconspicuous, do not expect it to be invisible. A seam in granite and quartz countertops will always be something that you can both see and feel. The color and pattern selected can make a difference as to the appearance of the seam. The least noticeable seams occurs with a light colors with a solid or very small pattern.
Once templated your fabricator will recommend the best location for a seam. They will take into consideration material sizing, countertop layout, and cutouts.
If you have a preference of the location of a seam, discuss the location when the fabricator is making the pattern (template) for you countertop. Be sure to be present while they are doing final field measurements, so you can discuss seam location.