For a while in college, the only knife I used was a Chinese-style cleaver. I could pretty much do everything I needed to with that knife, and it was comfortable. These days, I've got a few more knives, but the one I use most frequently is a 10" French chef's knife. It's all about comfort.
If you could test the knife out for a day or two before buying, that would be ideal, but how likely is that? At the very least hold it to see how comfortable it is in your hand, and how balanced it is. Imagine using it for common tasks.