Only you can make that decision, based on what you're likely to shoot and how you want to process it. As for myself, I like 4x5 and consider it a "sweet spot" because I can use my enlarger with it, and the film and holders get exponentially more expensive at 5x7 and above... not to mention the size and portability of the camera itself. Personally I'd recommend borrowing or using a friend's 8x10 before deciding if that large a format is really right for you.