This question depends on whether or not you're going to do any DeFi with FTM.Where did you buy fantom at really don't wanna deal with binance again
If you're just buying and holding, the easiest place to do that is Gemini, Crypto.com and KuCoin.
If you're going to be doing yield farming or auto compounding etc, then you want to get it from a DEX that supports the native FTM token
If you buy the ERC20 version of FTM on Gemini for example, you will have to pay gas fees if you ever convert it over to FTM's mainnet.