Muhle Silvertip Synthetic is the BEST. The other popular option is the Plisson Synthetic. I favour the 21mm (M) as it's a good all-rounder for face and bowl lathering.
HJM Black tips are best budget Synth.
Let's get this to happen!!!
Too many color/size options to add.
These are the best reviewed synthetic brushes I've read about, but there's not a lot of competition for modern synth brushes.