Shaving brushes tend to be a matter of personal budget, face feel, and lathering method.
Those who face lather tend to prefer fan-shaped or flat--canopy brushes. I bowl lather, so I prefer bulb-shaped brushes.
The more sensitive you skin, the softer the face feel you are likely to prefer. I have very sensitive skin and prefer silvertip brushes or at least two-band finest. Unfortunately, these tend to be more expensive than pure badger and best badger brushes.
For me the sweet spot in knot diameter is 24-26mm. I do not like smaller brushes, but some who face lather go as low as 18-20 mm. I have one 28mm Maggard SHD gel tip brush. That brush almost covers my entire cheek once it booms to full size. That is a little too large. I wish I had gotten 26mm instead. In some types of knots, 28mm would not be too large. The larger the knot size, the more hair is required, so the more expensive the brush.
Shavemac in Germany is a great brush maker. Bernd Blos now operates the company founded by his father. Bernd also makes brushes sold under some other premium brands. I own a Savile Row 24mm silvertip brush that is my personal favorite.
On the Shavemac website, there is a product advisor and configurator that describes various options and allows you to custom design your own brush. However, even if you do not purchase your brush from Shavemac, the descriptions will help you determine your perfect brush. Choose wisely!