well if you have $500 now and you wanna invest I will advise you to go for ETH. the coin has been pumping up for a while now and dont be surprise the price might reach $1000/ETH by first quarter of 2018. i can not advise you to buy BTC now because the price is very high now. Ltc has not been encouraging for a while now i do not see the coin pumping up any time soon. still around $72 for LTC. token market is not doing fine now but if you want to give it a short you can invest in AION. the token is already listed in two exchange website and it is also on coinmarketcap
This is very logical. Bitcoin is now very expensive it would not be wise to invest in it now. While ETH is now a lot cheaper than bitcoin it has also good potential.
Don't forget that there are also coins that are made of Ethereum itself.