Was in Mexico City last week. Went to the Cine Nacional, a huge suck cinema located about a 5-minute walk from the Pino Suarez Metro stop. If you depart at the southernmost exit, you're just right by the street it's on. Use google maps/yahoo business directory to find it exactly.
I didn't try any other cinema, so this isn't a comparison, just a quick report.
I went in and paid the 30 Peso (US$3) entry fee. It's 30 Pesos on Friday thru Sunday, 25 Pesos on other days. Not sure if it's closed on any days. A guy I met told me that Wednesdays are quite busy, though who knows why?
Anyway, I went in, and downstairs there is one huge theater, showing str8 porn. It's a pretty standard suck cinema, with guys who want a BJ sitting down and guys cruising/walking around, looking for someone to suck. Also in the back left corner, there are often small groups. In the back right, there is an area actually cordoned off(!) where the Tranny hookers are working. Guys who are interested in them sit nearby and wait.
Upstairs seems to be more gay, though I found more luck downstairs--YMMV.
I'd say the average stats of the place are:
30-50yo, in decent but not great shape. Saw very few muscle/young guys, though there were some. It's a really big place, probably 2,000 seats--I'd say on this Friday afternoon between 2-4pm there were 200+ guys there. There was definitely some fucking going on, so bring your own condoms.
I'd go back again!