Why should I use DeFi over other cryptocurrencies?

It depends on the type of investor you want to be. Buying cryptos as an investment is speculative. You're hoping the price goes up, but it could go down too; the market is quite volatile. However, if you're staking, borrowing, or lending with stablecoins in a DeFi protocol, you can eliminate the risk of volatility and earn stable yields. They both have their risks. Picking either of these investment instruments depends on what you're trying to accomplish and your risks/reward tolerance.