Is the widescreen more seriously cropped? Well, it depends. If the widescreen has only the top and bottom cropped it can contain more of the original than a fullscreen that has top, bottom and the sides cropped. But as zombie84 said most fullscreen versions are cropped widescreen versions. And the ammount that is cropped can even differ per scene in the same movie.

Red=widescreen, green=fullscreen. See wikipedia

http://img139.imageshack.us/img139/6933/super35andtechniscopezb7.png

I don't know what other film formats do this (I think none). I would always go for the widescreen versions. And yes, Super 35 is shot on 35mm.