Centralized wallet is wallet where you don't have full access over your bitcoin (no private key), but usually they offer service such as instant sell/buy bitcoin, bitcoin credit card or no transaction fee. (Example : Coinbase and Xapo)
Decentralized wallet is wallet where you have full access over your bitcoin (you get private key), but without much service because it's decentralized. (Example : Electrum and Mycelium)
So, Which one is better for you? Centralized wallet or decentralized wallet?
Decentralized wallet is better actually because we have the private key, we are the controller. but I don't use it honestly.
I use blockchain, I have the private key, and there is service, so between centralized and decentralized wallet.