Nowadays the best investment is that you hold that amount in your wallet as in the next month the halving will occur and with that the price will increase much faster and o a higher value.
I would try to gamble with them because you cannot do much with only 20 Dollar worth of Bitcoin you need at least more.
But you never know maybe you can turn that $20 in to $200 if you give it a try.
Yeah that is not a big amount to have and that amount we can afford to loose, so even I will try my luck in gambling, and if luck favors me then I can make some money from it and if I loose it won't make much difference.