in my opinion the best altcoin to invest now is ethereum, nxt and bch, because the three coins are very good value seen from the movement of the portfolio, so I suggest you look or carefully before buying and making a decision to trade.
If we talk about the best altcoin, then for me it is ether, it is still in second place and no one can outrun it even though they are trying to do it , ether have great prospects.