I've been on Mintpal almost since day one (I bought Mintcoins at 4 satoshi just after it appeared). They had one major issue (but nothing compared to cryptorush or poloniex) the following days and since then... nothing, nothing relevant (occasional shortage but this is all).

I'd did not try any other exchange since then and I am completely happy with them. Plus, Jason is very reactive. And considering the amount of problem with exchanges these last week, I think they are very concerned about security.
My favorite non-fiat exchange so far.