Choosing a platform for your Ajax applications isn't a trivial task. Dojo has just gone out and written up its thoughts on why you may want to choose their framework, which includes the following analysis, and a set of comparisons to Prototype, jQuery, Ext, MochiKit, GWT, and YUI. Give it a read, and let us know your thoughts.
Breadth and Depth: Dojo is the "full stack". Instead of cobbling together components from several different sources, Dojo allows each component to build on a trusted set of high-quality building blocks by providing integrated infrastructure and a wide variety of optional modules. These components provide good solutions to common user experience problems and can be easily tweaked to meet your needs. From pane-based layouts to client-side charting and graphing to data binding to a time-tested module system, Dojo is solid infrastructure for delivering great experiences.
Quality: Infrastructure for internationalization and accessibility is woven through the entire fabric of Dojo. Keystrokes are hinted correctly. The components all fit together as a cohesive whole. Everything is customizable easily with CSS, but very little needs to be tweaked to get a great looking UI nearly everywhere. These are the hallmarks of a system which has been designed and tested to deliver great experiences, not only to users, but also to designers and developers.
Performance: Dojo is used on high-profile, high-traffic sites every day and Dojo's build tools are a key reason why. Dojo's package system makes it easy to manage large-scale UI development projects and the build system layers on top to make your applications scream; all without code changes. Dojo also packs high-performance implementations of common utilties into its core, and the rebuild of Dojo for 0.9 focuses heavily on performance and reduced code footprint. The result is a small, tight toolkit that is blazing fast. Dojo's performance alone makes it an ideal platform to extend and build on.