I used to use fingers until I stopped using liquid foundation altogether. (I now use mineral makeup) I, too, found fingers to be better at blending. Then again, i never really had enough practice with a foundation brush.. i felt like it took so much longer to blend, and foundation is one of my least favorite things to apply so i just wanted to get it done and overwith quickly.

I do think that with a good quality foundation brush, you can get fantastic application, and the benefit would be not having to dirty your fingers. Cons would be having to wash your brush regularly.