My recommendation would always be a Kindle, even though I have a Kobo as well.
For those that don't 'free' their books Amazon have a better choice, lower prices, and no risk of buying a PDF if that's all the publisher sends to Kobo (and yes I know one publisher that does that, and DRM'd PDFs even though they sell DRM free epub on their own site

).
Amazon also have a better eco system as well, with Send to Kindle. Cloud storage, whispersync and wifi delivery of your own ebooks.
I like my Kobo but they can't and don't compare to Amazon overall.