If I were to choose one altcoin that might boom I would choose ETHEREUM. Ethereum has the most possibilities of booming after Bitcoin.
Ethereum is the most obvious and also the coin I would pick if I had to invest my money, if I did not have to invest then I would look for a coin that's performing not too well but has huge potential, none immediately spring to mind but probably something which is promising revolutionary tech but as of yet has little to show to support their claims.