There are some responses already, but I will offer yet a different one: From a technical viewpoint, middle-middle is best. The seat in the middle of the middle row.

The reason is because movie theatres need to get calibrated: The sound and the picture get adjusted for the best possible viewing/sound experience. This calibration process usually targets the middle of the room, because this ensures that even the edges will at least have a decent sound and a decent picture. Nonetheless the middle-middle position will be where sound and picture are optimal. You sit at the centre of the area targeted by the sound system and where are at an optimal distance from the screen for the sharpest picture.

Of course, that is theoretical. Specific movie theatres may have a variety of reasons to go for a calibration that favours different spots and whether people want to sit in the middle-middle is a wholly different question.