The difference is: (Will use big numbers just to prove my point)

In genesis mining, you invest $ 2000 for a 2 years contract and will receive something like 0,60% every day...so you will break even after 150+ days (Hopefully) ....if the value of the coin goes up meanwhile you will break even quicker.

In hashnest, you will not purchase a contract ...instead you will purchase a device like an L3 or S9 mine ...or a share of it. So the device is yours and will not expire after 2 years....so you could mine for 30 days and then sell you miner device for the same price that you purchase it or even more.....