Best currency to mine or buy

If i would mine - then i would mine new coins. Just have a look at the market and check what new coins are out there.
If investing with fast returns - of course i would go for ICOs and keep an eye on pump and dumps (buywalls/sellwals and all that stuff).

For the looooooong investment strategy, probably a mix of 10 cc including ETH, MON, Zcash.