I agree with Dr. Drib the best will be to see a unit for yourseft.
this thread is from people willing to show their devices:
https://www.mobileread.com/forums/showthread.php?t=26574
I'm a programer and use an iliad. I can read programming reference books in pdf format just zooming to eliminate the margins. For content you only have mobipocked.
I test a sony reader 505 and is a wonderfull machine but I found the 6 inch screen a bit small for pdf.