to get into slot canyon photography, I would definitely recommend lower Antelope Canyon. Be there early (usually in October they will be opening at 9) and expect to spend at least 2-3 hours in the Canyon - after that, around noon/early afternoon, the light begins to be a bit "flat". And yes, try to get a photographer´s pass (last time I was there, a DSLR and a tripod would have qualified you for this pass) - so you will be allowed to enter the canyon on your own, and you won´t have to stay with a group. When you get in there early in the morning (and maybe not on a weekend), your experience will resemble what it was like to visit this place one or two decades ago - until the groups will start entering the canyon.
Actually, October provides excellent light down there. If you´re interested, you might want to see some samples here
I decided to no more visit upper Antelope because of the crowds - photography (and even simply being there) is no fun any more. Waterholes Canyon, on the other hand, will provide you with a bit more of adventure - unfortunately the light is much less appealing there when compared to Antelope.
Another one that you might like (and which to visit certainly will have the appeal of a little adventure) is Round Valley draw which can be reached via the Cottonwood Canyon road, south of Kodachrome basin. However, please remember that Round Valley draw is not a simple walk-in like upper Antelope, but requires a bit of scrambling (and a short rope). Be sure to check the conditions at the BLM before going there, including getting the latest info on the road conditions of the Cottonwood Canyon Road, which these days appears to be washed out a couple of miles before it hits US 89 at its southern end.