Bookeen Cybook allows you to load any True Type Font and to interactively choose any of 10 sizes of the font. Sony (both the 500 & 505) allows you to select from small, medium & large. Not as nice, IMO, as the Cybook. For me this is enough reason to go with the Cybook because peoples eyes are different and a font that is easy for you to read might not be for me.
Page turning is slow but only about as slow as a leisurely turn of the page on a pbook. Neither one takes 5 minutes to turn a page, only several seconds.
In addition the Cybook has dictionary lookup capability.
There is a "Delete" button on the Cybook but they have not yet implemented it with their software. You have to connect to a computer to delete ebooks from it. I understand that the Sony PRS-505 has delete capabilities now on the reader.
No knowledge on the Iliad, H3, or Kindle.