The pocketbook are also 9" readers - if you look for Jbaach (a user on this forum) you will find a lot of videao comparisons of all matters of feaatures of the two. Onyx has a Pearl screen, the Pocketbooks do not, but apparently that is not too much of an issue (though I have never seen an Onyx, so I cannot really say - if pocketbook had perl, I'd take it
).
Colour is much better if you are using it for college, and if you have no experience of ereaders if I were you I'd first play aournd with one, as the speed of response is much different from a tablet. I strongly prefer e-ink, but my suspicion is that if you need it for college you'd be better off with a tablet.