I think I will go with the Sony.
I do need the expandable memory. I maxed out my memory on my Kindle. I have hundreds of fanfictions that are novel length, hundreds more that are short and then some very, very long fanfictions (one is 3000+pages) plus the novels I buy, free books, free short stories from authors. I didn't have a single audiobook on my Kindle and it took maybe 9-18 months to fill it up.