Decentralized exchanges are good and safe when you are in hurry but, from my experience, they are not that good when the network is congested because transaction fee + approval tends to go really high during that time.
That's exactly the problem with DEX, they ask for too much fees and we saw this during the hype of DeFi project. For me, the fastest and safest is through P2P transactions especially if you have friends that are willing to buy your coin/token. CEX are still safe though there are vulnerable to the hackers so don't put too much money to them. Instant exchange will also depend on the traffic in the market and will also depend on how much fees you are willing to pay.