I have a Sony and have recently purchased a Kobo Mini . . . and I love both! The Kobo Mini was £59 from W. H. Smith online and it is lightweight and very convenient for travelling or carrying around. My Sony - I find - feels more 'substantial' and I love the way that you can group books in series (so that books in a series are read in the correct order) Of course, Kobo might have that facility, but I am still learning about it as I have only had it a few days!
The bottom line is, I love both of my 'children' equally, but for very different reasons! Plus, you can read PDF's on either device!
I hope this helps a little, but it is a very subjective thing!