I use a two-step approach. I use Gemini for banking, and GDAX for trading. Gemini has free instant transfers, great support, and is fast on the ACH side. They don’t have as high of trade volume as GDAX though, so once my funds clear I move them over to GDAX to trade, and when I’m done there I send it back to Gemini to withdraw to my bank account.

Also one more benefit for trading on GDAX is that their maker/taker fee system is much more transparent than Gemini’s, IMO. I literally trade for free on GDAX which is much harder (or impossible?) to do on Gemini.