Anecdotally, I would say Rackspace has the most intuitive interface and good telephone support. They've just released new performance instances which are cheaper than AWS: $0.08/hr for 2 vCPUs, 2GB RAM and plenty of SSD vs $0.12/hr for AWS 2 vCPU m1.medium.
Our local VPS has fantastic customer service and we know each other by name.
Amazon has the real truly global infrastructure (Rackspace UK is a separate entity to US, ASIA) and Route 53 Anycast is outstanding.
We'll be trialling out Google Compute Engine to see how it fares.
For now I see Amazon for global DNS infrastructure, but I can't see Rackspace going anywhere.
Seems like Gartner have previous with Rackspace: http://www.theregister.co.uk/2013/11/20/gartner_openstack_cr...
Also interesting reading: http://gigaom.com/2013/12/20/backbreaking-openstack-migratio...