If you are using it alone, Arimidex is absolutely all you need. If you are using it with aromatising gear, I recommend Letrozole.
The good thing about Letrozole is that it is the strongest among Letrozole, Arimidex and Aromasin, so you can use a small dose for minimal estrogen reduction, or a higher dose for almost complete elimination of estrogen. The only downside is that some people get headaches from Letrozole. And complete elimination of estrogen is only negative, so it's good to experiment and find your optimal dose. If I eliminate all of my estrogen, I actually look flat because of lower glycogen levels and less muscle hydration I assume.