Difference between fan and bulb badgers

Why not the hybrid shape?
More effective than bulb in face lathering.
Easier than fan to build the lather.

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.

+1.  I think this covers it well.  When in doubt, I would reach out to the maker.  State your preferences and ask for recommendations.  I would also ask which knot/hair/shape is their most popular.

"I wanted to send a rather long reply but after several problems I learned that there is a limit on the size of the reply that I was nat aware of.  So, I will have to break it down to several continuous replies instead of one.  Bare with me."

I do not believe that a bulb has more back bone than a fan shape or visa versa.  What contributes to back bone as well as flow through is the knot size and the badger used.  What most people purchase is what I call off the shelf brushes.  Most manufactures such as Simpsons, Brad Sears, Paladin, Heinrich L. Thäter, Wiborg, The Varlet to name a few do not make true custom brushes.  They make a brush and sell to a reseller (with the exception of The Varlet) and you can not get a brush too you own specs.  There is few manufactures that make a few brushes a year and if you are lucky they may make you a custom brush.  However, there is one true manufacturer who make an enormous amount of brushes and will sell you off the shelf brushes as well as brushes to your specifications and that is Shavemac.  To begin with I do not want a beautiful custom made handle.  I am concerned with the knot.  The Varlet makes some beautiful handles which can take you months to receive and I am not interested in paying close to $400 for a brush because of the handle.

Now, getting back to backbone.  I currently own 17 brushes consisting of Simpsons, Thäter, Morris & Forndran, Wiborg and Shavemac.  All of them with the exception of Shavemac are off the shelf brushes.  Fourteen of these brushes  have a 26mm and 28mm loft.  Three are smaller which you will see in the following photos.  And only two are bulb shape.  Around 6 or 7 years ago all you could get off the shelf were bulb shaped but now you see more of fan shaped.

Shavemac will make you anything you want.  There is a difference between Pure Badged and Best Badger which is used on less expensive brushes.  There is also single band and two band badger where the later is a prized hair.  When I have Shavemac make a brush I always use either Silver Tip 2 Band or Silver Tip DO1 2 Band.  DO1 is a very stiff hair which generally produces more back bone.  But the the size of the knot especially loft has a lot to do with back bone and to a certain extent diameter.  Believe it or not I have certain brushes for certain soaps or creams and, the days I went without shaving.

The following three phots will demonstrate what I mean with three of my brush brands.  Photo #1 show my three Thäter’s.  The first two have a 26mm loft and around 50mm loft; the third is a 28mm and around a 51 mm loft.  I can not say that there is a terrific amount of back bone but it is like rubbing cotton on you face.  I only face lather and these brushes are perfect for certain soaps and creams.  I have 117 soaps and creams.

Photo #2 Are my Wiborg’s a combination of 26mm and 28mm.  All very similar to the Thäters But these have a little more back bone and again work well with certain soaps and creams.

Photo #3 are my prized Shavemacs.  With the exception of brush #1 which is an off the shelf brush all are custom made to my specs on handle, handle color, knot diameter and loft as well as Silvertip 2 Band and Silvertip DO1 2 band.  Brush # 1, 6 and 7 are Silvertip DO1 2 band.  If you are looking for back bone you came to the right place. Brush #1 has a diameter if 24mm and is very stiff; brush #7 is 25mm and again is very stiff.  Some people my be turned off by the stiffness of these two but work for me well with certain soaps.  Brush #6 is also DO1 but, has a 26mm diameter and 50mm loft while stiff it’s larger diameter and loft makes it a great all around brush for many of my soaps and creams and a beard that may be several days old.  Brushes # 2, 3, 4 and 5 are all Silvertip 2 Band, not as much back bone but perfect with all of my products.  Brush #2 has a 28mm diameter knot with a 54mm loft.  I can paint a house with this brush but is great for most creams.

So, in my opinion loft design has nothing to do with back bone.  The size of the knot as well as hair type does.  That’s my opinion and I am sticking to it.

I think this question is very subjective.

Personally, I like the high-density fan knots over 28mm very much. Because there's a better sense of badger wall.

But if it's a light bulb, I like it to be about 25-26mm. Medium density, badger hair must be soft enough to provide me with a dexterous experience!