I have a small contract on genesis mining and I have had no issues with them. They are very clear in their payouts and give you a lot of ability to choose where your hashpower goes. In addition, tours and pictures of their mining facilities are easy to find and they have a good track record of credibility. I currently mine bitcoin with them but am looking into getting an ethereum contract soon.
thanks for the reply. i was worried because i found many people talking about the payment: they say that in the first months you ll get paid but then it will be worse and you ll be not able to recover the money you spent.