To put another way:
The coin to mine is the one that costs less in power+hardware then the value of the coin
today.
the coin to hold is the one you predict will go up in the short/medium/long term.
if those are the same one, great. if not, do this:
I dont know much about mining but I have a cousin who does it and he mines small coins that I never heard of and then at the end of the month he trades them on coinbase for BTC and ETC
or think of it as 2 separate transactions. mine to sell, use the cash to buy what you want to hold