I have already visited the Upper Antelope Canyon during my 2008 "Grand Circle" road trip with Agnieszka. But as Anil has not seen it yet, I thought that a quick stop at the other slot canyon, called *Lower* Antelope Canyon might be a fun thing to do for both of us.
If you have been there, you know that it is a pricey pleasure. The guided tour to the Upper Antelope Canyon costs $32 per person and the tour to the Lower Canyon costs $25/person. There are much less people in the Lower Canyon, which makes your experience much better and the photography much easier. The Upper Canyon might be slightly more picturesque, but I think now, after seeing them both, I would recommend a visit to the Lower one over the Upper one.
Below are photos from the Lower Canyon, and for comparison here are photos from the Upper one.
A rather surprising entrance to the Lower Antelope Canyon:
It is easy to get mesmerized by the shapes and colors of the rocks inside the canyon: