Both are good for long term trading so it's up to you what will you choose. Both can give you decent profit even just by holding it. But since it's only $500 you won't feel profit that much unless their price will really pumped hard.

Since you are new I can't suggest you to proceed on other altcoins since it's more risky but the reward is decent if you play it right. I suggest to just build experienced first by doing experimental trades. Yes you need to risks a bit of money to get start. While holding you can practice how to trade on other coin that only requires small amount ($100 is enough). This requires analyzation so you really need to spend time learning.

If you are not comfortable taking a course to advance level at the moment, then just buy either BTC or ETH and hold.