There are so many promising alt coin now, since the increasing number of ICO. But I have some suggestion,
Ether maybe the only high-class alt coin that is still worth to buy,
In the mid-class I suggest Ripple and Lumens, I think they are kind of rising star now,
While in the low-class there are several coin like IOTA, ADA, TRX, that is still trying to find their way, but seems so promising,
Basically I just show you my portfolio, so maybe my opinion a little bit bias,