What do you mean - Stable coin? Tether is most stable, but it have not opportunity to grow. If you are looking to coins wich will not fall one time due scam, I think that first 50 by market cap are stable.
Tether is USDT that's why this coin is permanent stable. But this guys means another stable coins i think. First 50 coin are stable in coinmarketcap i think it's not correct because VERI coin price was around 500$ in january now it's price under 20$ you say it's stable coin? same coin is NEO huge up and down coin.