i dont plan on buying more than one brush, when i first started i bought a van der hagen badger brush, thats done me well, but i want to buy something thats quality and that would last me, i dont know if i should go synthetic or not, the price difference isn't much
In response to the question you posed, they don't. Much like a boar doesn't compare to a good badger, the same goes for synthetic, horse, mixed knots and whatever else you want to try and lather with. The fact is that all fibers/bristles have their own unique characteristics and will perform differently based on such. I have tried Gen 1,3 and 4 synthetic brushes and they have come a long way in softness, water retention and resiliency. However, they have a long way to go before I consider them a good replacement for my favorite badger brushes.
I cannot speak as how synthetic compare to boar or badger, but I am able to say that I have been happy with the Omega synthetic brushes I purchased.
I have Omega's Top of the Line Artificial Badger (AB) and Omega's Hi-Brush (Hi). The AB is a softer brush and as such, a bit floppier. The Hi has a little more backbone. The AB works better on softer soaps and creams, while the Hi is able to tackle all, even harder soaps. Both are easy to maintain which is pretty nice.
I may be wrong, but I believe the AB is more or less out of production, making it a little harder to find. Shoeboxshaveshop seemed to have the widest selection, while the Hi is in stock in most, if not all, online vendors.
For AB, I have Omega 643714 and 643186. As for Hi, I have Omega 0146206 and 0140652. Between the four, I use the AB 643186 the most as I use softer soaps/creams and face lather. If you are more for hard soaps, either of the Hi will work. The Hi tends to be more densely packed.
I have a Mayd-Well brush that was fully restored by Nick at www.sportshaving.com , it was originally a badger brush made between 1900 to 1920. It now has a synthetic knot. I don't know where he got the knot, but this is one awesome brush. It produces the best lather in both creams or soaps that I have ever seen. He (Nick) restores many brushes and is very good at it. If you like the idea of using a rare, and restored brush like this, he's the man. I have used this brush almost daily for over 6 months, and it hasn't even lost one strand, nor has it lost its firmness. His brushes are awesome to say the least. I even have one on standby in case something happens to this one. Nick takes a lot of pride in his restorations. In my honest opinion, his brushes are without equal.
I do NOT like the Muhle Synthetics I've tried (Black Fibre and STF2) as much as a boar or a badger hair brush. I feel that I can get a better and more hydrated lather from the latter two options. I also don't feel that horse is as good as boar or badger overall. YMMV. They all will make a useable lather, it will just come down to what you like. Synthetics don't hold heat and have a springy and fake feel to them. They get the job done, but they don't feel that great to me.