I d say

OMG
ETH
WAVES
DASH

In regards to MASSIVE gains (ROI)
It is hit or miss

My most promising and it already starts to show is Spectrecoin
I ve been a holder of this project cause they have promised to invent anonymous PoS

Means you can convert all your funds to Spectre to keep it "off the blockchain explorer" but STILL receive staking rewards on them (interest)

As of May 17th this technology finally has been implemented in v3 wallet and finally gone LIVE



The price has already gone up significantly
Yet, still many people don't know about it (its only TOP 200 as of now)

Is it private - Yes
Can you gain anonymous PoS rewards - Yes
Is it a good smooth wallet - Yes
Is it easy to work - Yes
Is it still unknown - Yes $