Traditionally, the best place seats at a theater performance are in the center orchestra section between the fifth and 12th rows. (Theater critics typically are given seats in this area but on the aisle in case they have to get out quickly to make deadline.)
But why are these "best?" You see the show from the persepective the playwright and director saw it. You are seeing the show the way it was created to be seen.
Lower seats in the mezzanine often place you above the 12th or 13th rows, so these are good seats as well and less expensive. However, you are looking down on a production meant to be seen closer to eye level.
Rest assured, the director and the producers have paced the house and designed the show to give the best view to the most seats. But center seats, close up are the best.
NOTE: The first three rows are less desirable because you are often looking up at the action and possibly missing some of it. Lottery tickets typically are first-row seats that are hard to sell.