Get the PDF if you want to keep it simple. You can read the book on any device. And it’s free.
If you have iBooks on your Mac or an EPUB viewer, get the EPUB version. It is .99 at Smashwords.
Got a Kindle? Grab the book at Amazon for only .99.
Can’t decide, or or you like the sound of “free ebook?” Just grab the PDF – it will work anywhere.