I think it depends on your business strategy. For example, if you live in New York and you are aiming at local clients, you won't want to be hosting servers in Mexico or anywhere in the south, so you can narrow down your search by location.
Also, bandwidth carriers is a big decision maker. You might have great pricing, great location, but what if the datacenter has cheap and non-stable carriers?
You want to check out the support and the features that the facility offers. For instance, do they have fast proactive support when one of your servers goes down? How long do you need to wait for an OS reload? Can you "self service" your account and servers (re-install, set DNS, reboot etc).
I would also be looking at other things too, ping rates from different locations, test files, public network status (if available), reviews etc.