You can choose from a variety of formats for your ebook, and each format has its advantages and disadvantages. Some formats are easy to print hard copies from and some are a major pain in the keester. Some formats are easy as pie to read on a phone, and some are very difficult to read on a phone. Some formats are good with images and others are lousy with images.
So, before you select your ebook's format, determine what the book needs to accomplish by asking yourself these questions.
Does the book contain worksheets that people need to fill out?
Who is your audience? Individuals forty and up are more likely to print stuff, and want to print stuff, than the younger generations.
Does the book have a lot of images? Are the images decorative or critical to understanding the text? The images look great in pdfs. Images can be readable and good on the Kindle and on tablets. Images don't transfer to smartphones nearly as well.
Are you going to create a lot of eBooks? Are you okay with an expensive up-front cost in money and learning curve?
How do you want to distribute the eBook? If you want to distribute the eBook on Kindle, readers have to go through extra, annoying steps to put a book on their reader if they don't buy it through amazon.