Coinbase Pro offers professional trading tools and services, delivered through a completely reengineered UI that will make the trading experience easier and more intuitive.
I stopped using GDAX a while back after I got screwed a few too many times by their server load problems, regardless, it's still missing a hand full of TA tools.
Pretty much use Coinbase Pro (formerly GDAX) for most of my virtual currency trading. Really enjoy the low platform fees and high trading volumes as it means I get more bang for my crypto-buck!