My favourite ride picture is from ToT. WE had one elevator with all Canadians who worked at the pavilion - dressed in red and white with maple leafs painted on our cheeks. It was our Canada Day photo.
The only I usually purchase, if any, is Splash Mountain. Especially when traveling with first timers. I think they anticipate the drop since they can see it from outside so they usually make a funny face - also it usually only has people from my party in it. I don't like buying photos of a bunch of strangers.