^^ This. Just make it into an .epub and let people use the reader they want.
I usually use Calibre to convert things to .epub for personal use, but I hear Sigil is the way to go if you want a professional quality product. Also, if you publish through Smashwords I think they can handle conversions to multiple formats for you (I'm vague on details, but I've heard talk about some utility called the "meat grinder").
I would suggest visiting Mobileread.com to see how other people are handling this. There are many self-published ebook authors there.
The only reason I can think of to make an ebook into an .apk would be if it was a specifically Android-related book, and you want to put it in the Android Market because your potential readers might not normally be interested in ebooks from the usual places. However, you would be cutting yourself off from other audiences.
