i'm still in the research phase... if you were just starting out, would you build a rig or just buy certain coins on an exchange?
It also depends on how much to you are willing to invest in trading/ building the rig and switching coins. Some people see building a rig as a hobby others like trading.
Buying a certain coin is more risky because you put all your eggs in one basket, when mining you can always switch to a new coin.