I think the majority of posters will tell you to get an 8" jointer. I only have a 6" jointer.. Then I realized that it was more than adequate. Most of my boards don't need the face side joined. The planer does a good enough job. I face joint so rarely that I don't mind ripping the board down the middle to fit the jointer if I have to.
The only thing I'd suggest is to get a 6" jointer with a longer bed. That has the advantage of letting you join longer pieces. In defense of the 8" jointers, they generally have longer beds.