Coinbase and Kraken are sketchy. They worked okay when the world was small but it isn't anymore. WA state and NY state passed laws specifically against sketchy-ass cryptocurrency exchanges; this is why Coinbase, Kraken and Poloniex have discontinued trading there. Gemini is compliant with 50-state law, so far as I know.
https://www.facebook.com/groups/Ethereum/ Not for the knowledge, but more for the lack thereof. But more importantly, I recently recommended both Coinbase and Kraken to people and they had horrific experiences. It's pretty clear that both exchanges are overextended and out of their depth and that's how Mt. GoX happened. There was no reason for GDAX to allow a 10,000 ETH market order. Neither you nor I nor anyone we know would be allowed to do a hundredth of that. But for some reason, GDAX let it through... which is troubling as hell.