Epcot for sure- so many places for pictures including World Showcase, the lake, Spaceship Earth and if you're going during Flower and Garden Show there are many photo op opportunities there too.
We did every park except DHS. We figured it would be so busy at DHS we wouldn't want to take the time to do pictures. Loved all parks. Our photographers were great and we took pictures in Italy. Really fun! eta: We might have considered DHS if they were doing ToT. I would also like to mention this was during Spring Break; super busy but you wouldn't know it from the pictures.