I use one brush. I paint everything with it. I have gone back and forth between Citadel (GW) and Privater Press. The brush I have been using is starting to shed. This means that it is losing bristles and getting a lot of bent bristles, which have to be trimmed off.
I bought the giant paint set from Vallejo five years ago. It came with several brushes. They are synthetics. There is a debate about synthetic vs sable. I'm not sure how there can really be any discussion on this. Sable is so superior that it blows synthetics out of the water. The cost difference is just not worth the difference in quality.
Having said all that, both GW and PP make good brushes. I have just worn out a PP brush, after using GW brushes for years. As it happens, when I went in to buy a new brush today they did not have the PP size I have been using. I bought the GW "yellow handle".
I hope it works out. I have a lot of painting to get done. I will use my just retired PP brush to paint the Quickshade on my Warriors of Minas Tirith. There are two schools of practice among dippers. (Perhaps there are more that I don't know about). There are the pure dippers who actually dip the models in the dip. This involves shaking a lot of excess dip off of the model, wasting dip, making a mess and making sore arms. The other school, to which I belong, paints on the dip. I avoid all of the above problems and it gives me more control over where the dip goes, and often more importantly, where it does not go. The draw back to the painting method over the dipping method is that it takes longer.
I did not realize how rough the old brush was looking until I held it up next to my new one. This should speed things up.