My favorite altcoin in 2018 is Monero, Cardano and Stellar. Monero brings privacy to the user, all transactions with this altcoin are anonymous. Cardano has advanced technology, professional team. It overcomes many of the weaknesses of Btc and Eth that this altcoin has good scalability. Stellar has impressive growth rates, I believe in the last few months of this year Stellar will grow rapidly and have high value.