I agree with SK, ROOT is GREAT for really testing against the toughest competition possible. My last 2 games have been against a National T1-2p champion (Soul Seeker-NY) and another of the most highly respected players in the country (Polarius-TN), and my next game will likely be against Alex_Olijar-PA, who is also highly respected around the country. Where else are you going to face competition like that from 3 different states?
*admitted bias in this post as I'm currently serving on the leadership team of ROOT