I use Coinbase just to link to my actual bank account and transfer from/to USD. For trading coin to coin in a stock market type exchange I've used Poloniex a bit, though they are having severe growing pains and you'd find the same issues you're seeing on Coinbase when timing of the trade is critical. If I'm just sending some Bitcoin from Coinbase to Steemit (converting it to Steem) Blocktrades has always been easy and great, no account needed. And finally I just started playing around with OpenLedger. It's the exchange that is powered by Steem's "sister coin" Bitshares. It's really interesting. Pretty complicated to get to grips with but well worth it. It's a decentralized automatic exchange. I don't know why more people haven't switched over to it from places like Poloniex.