The big buzz word these days in the data center world is Tier 3, Tier 3+ design, Tier 4 ect...
Did you know that there is not a single tier 4 data center in the USA that offers public colocation? In fact according to the Uptime institude there is only one yes 1 Tier 3 certified facility in the USA.
There are some very good facilities that are not Tier certified that offer good services, but be careful of operators claiming Tier 4 design. To be considered Tier 4 you must have two primary power feeds online. Yes a lot of facilities have ATS (automatic transfer switch) but this is still a single point of failure. One other issue I had confirmed and worries me is that Tier certification only pertains to within the four walls of the facility. So a data center could have fiber, copper, and power coming into the facility on telephone poles. Which makes me ask another question - is the Uptime Institudes Tier certifications focused too much on power?
We use Internap because of the network and track record for uptime at all their facilities, but they do have good redundant power and cooling infrastructure especially at the 1301 Fannin data center.
When planning colocation for your company do some research on the facilities but also be realistic with your service level needs as to not under or over provision.