Antelope Canyon is on Navajo Nation land, and Navajo Nation Parks & Recreation allows visits only with a guide. So every trip is a tour, sold by a handful of Navajo-permitted operators: Upper Antelope Canyon from Page or the tribal park gate, Lower Antelope Canyon by two operators on Highway 98, Canyon X by one, Secret Antelope Canyon off US-89, and the lake end of the canyon by kayak from Antelope Point.
Which one is right depends on whether you want the light beams or the stairs, how much walking your group can manage, and whether you are staying in Page or coming up for the day from Las Vegas or Phoenix. These pages compare them plainly.