I had a terrible experience with Nexcess.
I have 2 main sites using Magento 2 Enterprise edition.
I wanted Nexcess to host both of them and signed for a plan that should be strong enough for both.
I decided first to move only one of my sites in order to check the performances. When I did so I noticed that although it was the one who had less traffic out of my two sites, it was substantially slower than the one who hosted on Rackspace on a plan that cost half of the one on Nexcess!
We tried with their support team to improve things but they never succeeded to match the performances of the Rackspace one (not to mention that they were supposed to be better because of the twice more expensive plan!).
I asked to cancel and was told that I have a one year contract that I cannot cancel. So I had to stay with two plans because did not want to move my other site to the weaker environment. At the end of the year contract I told Nexcess that the year ended and I want to move all to Rackspace and I was told that I'm six days late in my response and that they already did their yearly plan and that I have to continue for an additional year!
They forgot that I wanted to move before, they forgot that I signed only for one year, and that if it was for two, they have proposed me when I signed a better price from day one and I said that I want to pay more and to commit for only one year.
At the bottom line their servers cannot match the leading hosts and the company isn't honest.
So be careful. Review collected by and hosted on G2.com.