Brass in an excellent conductor of electricity, but oxidizes readily. Unfortunately, the oxide is a poor conductor of electricity. Nickel-silver conducts electricity well, as does its oxide. You can use brass, but be prepared to clean it often, perhaps everytime that you wish to run a train. This is a nuisance, but do-able on a small layout, like a 4'x8'. On a room-size layout, such as the one I have now, I'd never have time to run trains if I had to clean the track before every operating session. As it is, I clean it only if I have been making scenery, and then, only in that immediate area. Nickel-silver generally costs more than brass, but, in my opinion, is well worth it.
Wayne