I can vouch for progressive mining, I hold contracts there and they are paying, except they are not very clear about your equivalent hashing power and only show u the company's hashing power.
but contractbtcminer is extremely fishy.
They have copied the contracts from progressive and did not even manage to change the name XD.
My advice? I think CEX.io are doing good, you directly buy GH/s and you can sell them just like shares/bonds