Personally, I would definitly include at least one night in Iguazu falls ... it really is very, very pretty. It is not the most strenuous of hikes (ok, it is pretty easy) but the views are just amazing and my wife (who also loves photography) had a blast takin' a bunch of pictures.

We never made it to USH, but we did make it to El Calafate and hiking on the glaciers as well as going on a 4x4 trip up in the mountains above the city. I have to say it was also very, very pretty. I would highly recommend it if you like hiking and taking pictures as there are tons of opportunities there to do so.

Drek