Generally it is depending on how much money you have to invest in cryptocurrency.
Things to consider/take into account as a speculator:
If you speculate, the luck plays a big role in the game, but if you are a miner, the luck plays a much less role in the game. You can even calculate your earnings (profit) at some extent in this case. It is depending on the situation and on the cryptocurrency. You can get a relative steady income with mining, but you can win (or lose) a lot with speculation.
For example: If the current value of a cryptocurrency is $0.01 USD, and you buy 1000 of it ($10 USD), then the maximum you can lose is $10 USD. That is your investment and risk at the same time. If the price of that cryptocurrency goes up even to $0.02 USD, then you doubled your investment.
Things to consider/take into account as a miner:
If you buy an ASIC miner, for example the Bitmain Antminer DR5 (34Th), which price is currently $1260 USD, then your initial risk will be $1260 USD, but that risk will be reduced as you mine Decred (DCR) and you exchange it to fiat money. It will (probably) turn into profit over time.
The risk can also increase as the miner consume electricity. The power consumption of the above mentioned miner is 1800 W, which is 1.8 kW. The price of kWh in the USA is approximately $0.12 USD. Let's assume that you don't use it 24 hours a day. If you use it for straight 5 hours a day, then that will be 9000W, which is 9 kWh (daily), which costs approximately $0.60 USD (daily). That is $18 USD for 30 days. You have to make more than $18 USD monthly to be profitable in terms of electricity. The current (2018.12.22, 18:10 CET) price of Decred (DCR) is $18.06 USD, so according to the current price, you have to mine approximately 1 DCR per month to be profitable in terms of electricity. So even if you get a miner FREE, you still have some risk.
According to the asicminervalue.com, the current income per day with the above mentioned miner is $14.60 USD, the daily electicity is -$5.62 USD, and the daily profit is $8.99 USD. The monthly income is $438.13 USD, the monthly electricity is -$168.48 USD, the monthly profit is $269.65 USD. This means that it will take approximately 4.68 months to earn back its cost, then the profit will (probably/hopefully) come after that.
But a lot of things is depending on the price of Decred (DCR) in this case (or the price of the mined cryptocurrency in any case), and no one knows what the future price will be. If the price will go up a lot, you get get into profit (much) sooner, but if the price go down much, it can become unprofitable. So this is also a risk factor.