This is a very subjective matter, and there isn't a one that is better than the other. All things to shaving comes down to the subjective opinion really. Certain characteristics do work better for certain things usually, though even with this with time you will find exceptions. Bulbs are usually preferred for working with shaving soaps thanks to increased backbone to the bulb shape, and many a face latherer likes it as the bulb shape helps keep the knot compact on the face and offers a bit more backbone. Perhaps backbone isn't the best word for it entirely, it's just more compact. Fans typically splay out a bit more and allow the lather to mix better, but come at a slight cost to control. Loft size, what bristle is being used, and knot size and density can affect this too. Even with the spread I usually prefer a fan or a fan hybrid as the lather generation is a bit better, and I really can't think of any fans I have had a problem with the knot shape. Sometimes a bulb gets a bit too pointy for my preferences. You truly can get the whole range from any brush regardless of construction. I'm more likely to purchase a brush nowadays if I get to see the exact brush for sale, knot and all. At this point I have a high degree of success of knowing whether I'll like the brush or not that way.