I am very happy with the note-taking and dictionary functionality on my Kindle. I find it really easy to use.
I'm trying to improve my German vocabulary through reading and it's a great help to have quick lookup of words within a book. There are issues with dictionaries with input languages that are not English though, i.e. German-English or Frensch-English, but they're not necessarily insurmountable:
https://www.mobileread.com/forums/showthread.php?t=60103
The biggest downside to the Kindle IMO is that it can 1) only read mobi or prc files natively, and 2) only use DRM'd books from Amazon - and Amazon is not necessarily the cheapest anymore. Unless you are prepared to de-DRM, and perhaps convert, books you buy in other shops, the Kindle may limit you.
I don't have the Sony 600 (the Touch) but I think it also has note-taking functionality, but I don't know how well it works. It has a dictionary, but I think it's only English-English.