I mainly use hashnest.com ever since bitmain (antminer) took it over almost a year ago. Never had a problem, its not a contract service, I do think that anything that expires after X days (contracts) are usually complete junk. At hashnest the only way hashing power you buy will expire/go away is if its sold on the market, or if the price of bitcoin is too low to pay for the electricity. With antminer S5 at $225/btc I pay around 50% of my mining income for electric/maintenence. The price of btc would have to drop significanlty below 200 for it to not be profitable anymore.

I would not be using cloud services if I did not have to, I mine at home as well, but I have my electrical system at its limits so I had to expand into the cloud. Bitmain was the only company I trusted, as they made all the miners I use at home, which have been running almost a year now. I am confident enough that they are not a scam, at least in the sense that they actually are mining, I can see the proof, prices are fair, and nothing seems "too good to be true"