I use both Rackspace and Linode. Both have been pretty good but Rackspace has been phenomenally reliable - I'm talking 100% uptime for the past couple of years (according to Pingdom) for my main service. Linode has been less reliable, though not bad by industry standards. I am planning to launch a new product next year. Will definitely be using Rackspace for it - that reliability is worth the extra expense and lower spec.