Desktop PC (work related PDFs and manga)
Laptop PC (work related PDFs and manga, tried Amazon Kindle for PC)
Nokia E90 Communicator
Nokia N900 (current phone)
Irex DR1000 (PDFs almost exclusively now)
5" Astak EZReader Pocket Pro (non PDF, non work related reading)
On my desktop and laptop I read PDFs related to work and manga, since the manga doesn't do as well on the readers. I also have Kindle for PC on my laptop so I could test it.
I started reading ebooks on my phone and have gone through several. I liked the Iliad and then got the DR1000 for PDFs, and then the PocketPro for general reading. I still use the DR1000 for PDFs as it does a great job displaying the full size. I now use the PocketPro for all my personal reading pretty much exclusively. The DR1000 was nice as I got a lot of text before a page turn, but it's big and a pain to carry around.