If you want to trade OP, the best, most trustworthy and reliable (as well as economical) option is Binance. They are a leader in the industry, they have really high liquidity on all assets, their security is solid, they are an institution instead of a a flash in the pan.
Coinbase is a brokerage and so the fees there are higher, but they have their own exchange called Coinbase Pro, which has much lower fees than the brokerage, and has a really good infrastructure.
Binance is a better option than Coinbase Pro though IMO. Trading at either Binance or Coinbase Pro is much cheaper than LocalBitcoins or out of any kinds of software wallets because they have way lower fees because they have a much higher volume of trades (so they don't need to charge so much).
LocalBitcoins is great for one-off trades where you need to get a bridge between crypto and fiat (mainstream banking or cash), but as a long term solution for making multiple trades it is a TERRIBLE option. You get shitty exchange rates and then fees on top. Exchanges give you close to the perfect exchange rate and then way smaller fees as well.
Binance is quick and easy to set up, and has industry-leading features throughout. It's the best choice for casual traders.