The intellisense feature is, in my opinion, the best by far. If I can't remember something all I need to do is start with a < and check the options.

I love how configurable Aptana Studio 3 is regarding UI style, how it lets you manage several projects and remote servers in tandem. The per-project Git integration is a bonus. The deployment wizard is really handy for hooking a project up to a remote server in no time. The built in console is excellent, and I use it primarily for Git, and navigating projects that contain multiple Git repositories. The Open Resource tool (Ctrl + T) and Open PHP Element tool (Ctrl + Shift + T) are great for navigating files/classes across all projects. The outline view is great for quickly navigating classes by their method names and allows quick identification of method visibility and scope. Code hinting and navigation for simple to intermediate purposes works really well. Tool tips are shown for built in PHP functions, too, outlining their documentation. It gives me everything I need to start working in a local development environment (aside from, of course, an HTTP server running PHP and a database server).

As a front-end designer, Aptana attracts me as an ultimate development IDE with many built-in features. I find useful remote connection manager, terminal emulator, PHP and Java runtime, Git support. There are plenty of add-ons in the repository, and highly customizable workspace is a plus too.