There is never a good altcoin to invest in longterm, stick with btc longterm...

Some coins have big potential. Some will develop enough to implenet into real life payments, but we have to wait and see which will it be.

potential is not enough, btc is most safe becouse of capitalization. even if something will go wrong on btc, you have time to react

alt coins are good for short investment. e.g. nectar coin for now