The whole stretch is touristy, they are pretty much all within a few miles of each other and can be busy. Take the Historic Highway and you'll be able to access any of the major falls. Some of the stuff takes a bit of hiking, but not too much. However, it's hard to hit all the interesting sites if you've only got an hour or two. The short list I'd look at would include:
Elowah Falls as mentioned above... scramble down below the trail for more interesting foregrounds.
Fairy Falls above Wahkeeha is small but very pretty, bring a wide lens.
Ponytail falls above Horsetail is a relatively quick and easy hike, probably a bit less photogenic than the others on the list.
Wahclella falls is a bit farther down I-84 but also a very pretty hike and quite photogenic.
If you're the adventurous sort, bring some shoes/pants that can get wet and wade up Oneonta Gorge to the falls at the end.
Women's Forum viewpoint above and west of Crown Point is the iconic shot of the gorge and best at sunset. If you time it right you can catch this on your way home.
Enjoy your trip!
