If you have a large rig that will require a lot of electricity & maintenance costs then maybe the best approach would be to mine profitable & established coins and then sell them (but still keep a few in case the price skyrockets).
The reason why I would chose established coins is that you have a lower risk of them going bust (or devaluating fast) before you sell.
If you have a low range mining rig I would mine and hold in case the price jumps, thus speculating on the price. Of course, you need to do your own research on the coins you select to mine, otherwise you will end up with nothing.
this is basically applied and a wise move for me, set aside rigs to cover your costs, Electricity, internet and rentals then the other rigs for coins long term HODL. either way you wont regret when Alts goes to moon again.