Choosing an exchange is solely dependent upon your trade requirements.

Sometimes the coin you wanna trade is listed on a particular exchange, sometimes there is volume on the other exchange, maybe your KYC doesn't go through, so you went with the exchange without KYC requirement, many believe in decentralized exchanges, many want to trade with real money so they either go for P2P or exchanges which accept credit cards etc etc.

All I want to say is we can't tell which exchange to choose. If you are only interested in trading some major pairs like coins in top 10, then go with high volume exchanges like Binance, Bitfinex etc. Whatever exchange you choose, make sure to read its review and check its volume. Before depositing anything, make sure they don't have KYC requirement for withdrawing.

Be safe!