unless you are looking for an exchange service to use not an altcoin to invest then you are posting in a wrong board. you should move your topic to speculation board.
if you want an exchange service then take a look at kraken, bitfinex, bitstamp, poloniex and bittrex
and my suggestion for altcoin is that if $50 to $500 is all your investment, in other words all you are willing to invest in trading markets then go with bitcoin 100% because it is your safest option as far as price rise and profit goes. other options have higher risks and needs you to be a trader.
if you can handle the additional risks, then invest 70% in bitcoin and the rest in multiple altcoins. litecoin and monero and ethereum are the hot coins that have big market that you can make good profit. there are lots other smaller ones but with them a higher risk also comes.