For me, that had to be Ripple. I traded for 100%+ thrice and still holding a position at $0.40.
My next coins are:
1) Ripple
2) ADA
3) Bitcoin
4) Ethereum
What's yours?
Ethereum to be honest. In my accumulation of Ethereum from the day I started getting serious into crypto until now, this is the crypto that I made the most money from. Bitcoin is just second and the rest are random altcoins that I have invested, traded or acquired from airdrops and bounty hunting.