I would cross off portability, we all want that and pretty much all readers are very portable
If you want, download the Sony software on your PC, and import some of the files you'd like to read to see how they turn out and get Calibre for converting, see how you like it.
Pretty colors- I love them too. I have a blue 505 (dark blue) but I bought some beautiful cloth covers that give my 505 some pizzazz