hashflare.io is pretty safe.
But if you look here, you'll notice that right now the best contract have payback period of 813 days. So it's more than two years just to break even. Most of the contracts (all timed ones) never pay back. For example 1-year ethereum mining at hashflare.io will give you net loss of around 30%.
There's a certain economical model. It would be profitable to mine if prices rise, but in this case more people will start mining, which will affect difficulty and make mining less profitable again.