I prefer poloniex, it seems pretty reliable with good volume and a live trollbox. I have also tried bittrex, but for the smaller coins the volume is sometimes is too low and the manipulations seems easier.
I use poloniex too,it is simply amazing for me,and i have no problems with using it,as same with withdrawals.And yes,trollbox is pretty good but too many trolls there want's you to lose money hahaha
Trading life ;P