Based on my experience, I think the most legitimate bitcoin mining company is genesis-mining, as they have their own mining rig and active in participating at conferences regarding cryptocurrency and blockchain. But you can also check Hashflare, Eligius, Slush pool, BTCC, GBMiners, and Mining Hub. I will not be posting here referrals from these sites, so it is up to you to do your research and see if you really want to try them or not...
Genesis Mining is the largest cloud mining company on the market but there's no legit cloud mining company because they end up scamming their users and the same genesis company have been accused of scamming their users. Besides, if you ask any member on here who's moderator,Legend or hero none of them will advice you to invest into cloud mining site because they are all ponzi site.