I must have to agree too that yobit is the worst support ever than those mentioned sites, their support takes weeks and even month/s before they contacted you back with the support ticket you made thats why you need to avoid this exchange so you can't experience what others did before. 
Same thoight. Yobit takes even month based on my experience just to fix an issue I encountered on trading. Responses are not professional and bad custkmer service overall. Next is polo and their security is becommkng shitty. I haven't tried other exchanges besides this two and bittrex and c-cex but I never encountered problem in the two so yea.