The title of the post gives it away, really. As fans, most of us are fascinated with the varying degrees of difference between each of Bowie's albums as they're released. Those who have followed him for a long time will be particularly familiar with this - catching up on his back catalogue, randomly or not doesn't quite give the same 'shock' or surprise that fans felt when listening to each new album. There are too many examples to list, and you know them anyway.
However, I'm intrigued by the question (and even more so at the countless possible answers) - of all his studio albums, which two can be described as the most different from each other?
In deciding, you could consider various factors - gap between the albums (large or small - a small gap in time yielding two very different albums can be considered perhaps to lead to a greater difference than just the time factor - i.e compare 'David Bowie' to 'Reality' - bound to be different cos there's 36 years between them).
You could also consider the music industry at any given time, nature of the fan base, impact of World tours, current musicians, success (or lack of) of previous album, whether an albums reflects a period/style/genre or predicts it.
Perhaps you'll go for Space Oddity and TMWSTW - small gap in time, huge difference in writing, music, etc. Or Let's Dance and Outside - maybe they're as different as you can get.
The choice is yours - what's your view?