Same question as in topic.
Where you invest your money today?
Btc, Ltc, Eth, Lisk or what?
For now I would say that investing by buying as much bitcoin as possible. You can see it now, bitcoin prices continue to increase every time. We can fold 500USD into 1000USD very quickly. Trading bitcoin is a very careful job.
Investing all $500 to bitcoin is very safe but to quickly fold 500USD into 1000USD you will need a long time because the price of bitcoin now is equivalent $5800 to your $500 become $1000 then the price of bitcoin equivalent $11,600 and i think this is just reach in 2019.
With $500 you should invest to altcoin like NEO, OmiseGO, Firstcoin, Waves that can bring to more many profit than bitcoin
Special you should research Firstcoin that seem bitcoinnect coin and increasing price very fast