You can't tell for sure, although polkadot is one of the best coin to invest, reason been that  is well known and many investors like using polkadot to invest, and a lot of people are also profiting from polkadot.but I can't guarantee you that polkadot has a brighter future, reason is because I don't invest on polkadot, i still want to make a proper research about polkadot  before I can't give any guarantee.