No one knows which coin can give promisable profit in 2018 because I hope no one have the ablity to predict what will happen in future.
So I will say Ethereum or litecoin which is the altcoin for now because these are most stable currency when compared to any other.
Will Litecoin survive when they release the lightning network? Are there other advantages except faster transactions?
in case you didn't know litecoin also has Lightning Network and soon it can be used in the same places that accept bitcoin if they implement things like Atomic Swaps.
and if profit is all that concerns you then almost all the altcoins are options because they will get pumped at some point and will give you good profit. this topic seemed to be about more than just dumb temporary profit though.