It depends

You either try to mine something what is profitable straight up, and just dump coins to cover your costs.
Or mine new coins and support the project behind them, but you most likely not gonna get much back for a long time might even be years. And there is always the possibilty of bust.
My advice would be to read a lot about different coins and there communty. The more active communty the more likely you will see your investment return.

ATM I`m into POLY/CSC(CXX) not really mainstream coins they just fit my low computing power (GTX960)