when you say online, you mean a custodian solution with
KYC right ?
you can custody your USDC directly with the issuer Circle. there you can exchange for fiat and transfer to your
bank account. they can offer up to 10.75% interests on your USDC deposit also but there is a waitlist it seems.
The world's leading digital dollar stablecoin.
www.circle.com
otherwise personally I trust and use
Kraken and Coinbase is also trustworthy, they both are fully regulated. Bitstamp is on the same boat and also Gemini.
I trust
Binance but they don't accept US citizen so much less regulated than the others, but offers much much more services !
if you are resident in EU Binance have a kickass crypto visa card.
perhaps try to be more specific on your requirements and what you want to achieve, its not very clear.