This is a very personal question. As you already have a device, you have some idea of how you use it, want to use it, and the advantages and disadvantages. One thing you want to keep in mind is that Kindle locks you in. If you just want to get the books, you could try Kindle 4 PC and then the script by I (heart) cabbages that strips the DRM. That way you can load the books into Calibre and into your reader. Of course, that requires multiple extra steps. With a Kindle, you buy the book and a couple minutes later your book is on your Kindle
What do you want and which is most convenient for
you!