I recommend using $ 700 to invest in Ethereum, this is the queen of the market, it promises to bring a lot of profit for you in the future. $ 400 next to Stellar, this altcoin is a new phenomenon in the market, it has impressive growth rate, I guess that the end of this year its price will be very high. The last $ 400 for Monero, this is altcoin worth your long term investment, it gives perfect privacy to the user. All transactions with Monero are anonymous.