2. Publisher (I will not buy anything from MacMillan)
3. Geographical Restrictions
4. Price (I rarely spend more than $5.00 for an ebook never over $10.00)
That's the practical side of the equation, now for the emotional/subjective reasons:
1. Author (There are a handful of authors that go on my automatic buy list unless the book conflicts with my practical list.)
2. Decent book sample, especially important if I'm not familiar with the author
3. Genre (I read mostly science fiction, fantasy and romance with the occasional technological thriller thrown in. I don't read mysteries even though I gift them to my Mom.)
I have many books on my wish list, just waiting mainly for the price to go down.