I have a K3 and a M92
2- screens: Screens are the same quality. Webbrowser of K3 displays text more darker than M92.
In PDF etc. they are the same
3- user experience: I hate Kindle list view without folders. That's why I love M92 - simple file management like on PC.
Kindle 3 responds to inputs much faster than M92.
M92 loads web pages much faster
K3 connects to wifi much faster
PDF on M92 is the best if you need scribbles. Kpdfviewer for Kindle does almost the same job - just no handwriting.
Overall: I don't like having 2 devices, but I can't decide which one is better. You have to choose for what application you need the ereader.