These are very different devices that ultimately do the same thing. I am a documentary photographer/film maker and I also have a hobby of making field recordings.
I currently have a Roland R-26 previously a PCM-D50. The R26 offers me 6 channels and two XLR's.
My current line of thinking is that the D100 is insanely high quality for inbuilt mics, and I could also use my Lav with it. And the 633 is almost everything that the D100 is but requires external mics and a larger bag. being a photographer means having a bag with cameras and lenses batteries etc, adding a D100 to that is nothing, but adding a 633 to that is additional batteries, mics, cables etc..
Im just not entirely sure which direction to go.
Lets not talk about the cost factor because we all know how much these things cost and the difference between the two items.