Hello and welcome to MR. I can't comment on the Kindle, as I have never owned one. I am quite happy with the way my Sony prs-505 handles the reflow on PDFs (I often read academic articles on it, as well as text-based academic books in pdf format; I would love to additionally own a larger screened reader, however, for home use) and if I were to buy another Sony reader I would get the prs-900, which, I have read, handles PDFs very well, and has some sort of margin crop and zoom function; apparently, if you read PDFs in landscape mode you don't have to zoom at all as it divides the page into thirds. I'm holding out for a larger screen for now, maybe a 9.7 inch screen, as it seems that several are scheduled to be released this year; however, I imagine that most of them will be quite pricey. I don't envy you, there are so many readers on the market now that it is hard to choose which one will suit you the best. I have pasted a link to the MR wiki page that showcases a graph of most (if not all) of the ebook readers on the market. I hope it helps.
https://wiki.mobileread.com/wiki/E-book_Reader_Matrix