There are lots of options how you can buy Crypto – here I list the options I have tried and still use.
Kraken. Low fee exchange. You pay only 0.2% fee for trading. If you reach bigger volumes – the price goes down. The only drawback is quite difficult registration process. (same is with Interactive Brokers for stock trading)
MetaMask wallet. I use it with Etherium network – so you can deposit ETH and USDT. They use mainly UniSwap function inside the app to swap the currencies. I also buy NFTs over OpenSea or LooksRare, connecting the MetaMask wallet.
Gate.io. You can only deposit Crypto. You can not deposit EUR or any other FIAT currency. I use this service for rare altcoins to purchase over in exchange to USDT. Another advantage of Gate.io is that you do not need to do KYC – so the registration is very simple. They have margin lending function. ALCX lends for 18% APY, AVAX 6,5% APY, and Bitcoin you can set the minimum at 3,5% APY, but actually the supply is so big, so that BTC is sitting idle.
Crypto.com. I have account with them as i think it is one of the best bank cards now. I do not buy crypto there as they charge 0,4%, but i do get CRO tokens there, where I exchange to Bitcoin and lend it at 4.5% anual interest rate. (user referral code: 5g6fg7z7wg to get 25$)
Revolut. If you have Revolut account – it is the easiest way to start. The fees are 1.5-2.5% (10x more expensive than Kraken)