FBreader is my choice, it even reads .mobi (which I think is what the Kindle uses) files which choked Aldiko. Nothing wrong with Nook, Kindle or Kobo but you basically have to give them a credit card number to function it seems. I had a B&N gift card and tried to use it and they refused to allow me to purchase a Nook Book without also giving them my credit card info (which I'm sure they use for DRM)
I like Aldiko. The app, when opened looks like a book shelf, plus it reads EPUB books. The best thing about the EPUB format is that you can go online and download free software and make an EPUB book for yourself to read on your tablet! I was able to find a physics book for an upcoming class online in a pdf format - I opened it with the free software and saved it as an EPUB file, put it on my tab and now I have my book (complete with hyperlinks!) ready to go before class starts.