The best altcoins can be around here now like eth or ripple but what or which will become the trend of the future is no one knows. For me, the best altcoin will always be eth because it is the most used and developed altcoin and it is just keep getting better even Vitalik has now left the team.
I think that in reality Vitaly Buterin will not be able to affect the ethereum badly, even if he leaves. can give a similar example, when Apple did not work worse after the death of Steve Jobs.