QB Desktop installs on your computer and used to be the least expensive with a low one-time purchase price. 

QB Online is SAAS paid monthly with more automated features but I don't like those since I prefer more control since I am an accountant and know what I want to do so don't want QB to make those decisions for me. I think Intuit's goal may be to move everyone to QB Online and last I heard they were increasing prices on Desktop.