There are countless yield bearing stablecoins and curated vaults where you can get good APY, but there is always going to be some counterparty or smart contract risk. Without leverage you are unlikely to beat Bitcoin’s price appreciation with stablecoins. The safest investment in crypto will always be buying and holding BTC.

If you really want to have some of your portfolio in stablecoins, then lending on Aave is probably the safest way to go. One caveat is that you need a really large investment to see significant returns as yield is typically on the lower end of the 5–15% range.