I don't know about the Coinbase issues. I think I made an account ages ago but never used them. I have never had any major issues that would worry me with Bittrex - certainly not like Poloniex.
Only used Kraken a couple of times so can't really render a verdict other than saying their UI leaves a lot to be desired.
Personally I use Bittrex because they have given me the least problems and any even slight issue I had they responded within a few hours - sometimes even when it was because I had cocked up.
I should just say though that putting your coins on any centralised exchange carries some risk.
Only keep things on for as short a time as necessary.
Hope it helps:)