If industry-leading uptime and rapid-scalability are your two biggest concerns, cloud hosting might be just what you're looking for. Cloud hosting will get you access to a cluster of servers from which you can quickly provision resources when you need them. Along with having enough separation from unruly neighbors, your application should be kept safe. VPS and Cloud services are sometimes combined into a hybrid service called Cloud VPS or Scalable VPS.
Many services offer a low "starting price," but require you to prepay for two or three years of service to get that price. After the promotional period, the renewal price for some services can be two, three, or even four times the initial promotional pricing. While the initial deal might be incredible, the cost of transferring your site (or paying the added fee) in a couple of years may be something to consider.