The differences between these two plugins are varied but subtle. After having used phpEclipse for the last couple of years, I decided to give PDT a proper try as I needed to do a fresh install in order to get the PHP CodeSniffer Plugin working fully.

PDT

• Excellent HTML validation, and built-in CSS support (code highlighting, intellisense and autocompletion for both)
• Good JavaScript support (code highlighting and syntax checking. However it often reports bogus errors when JS is embedded in HTML)
• Jump to file by right-clicking and choosing 'Open Selection' e.g. to open a HTML page referenced by a form action attribute
• More informational 'Mark Occurences' feature. The Mark Occurences is feature is one of my most used Eclipse features. It highlights all other occurences of the variable or function at the current cursor location. Usually that's all there is to it, but PDT highlights occurences differently according to whether or not they are read or write. This means you can instantly see the other locations in a file where a given variable is written to. This comes at a cost unfortunately, and if a file contains any parse errors the occurence highlighting will not work in PDT, while phpEclipse is not affected by such things.

phpEclipse

• Fully functional drag-and-drop - you can select text and drag it with the mouse.
• Richer code highlighting - e.g. single quoted strings can be coloured differently to double quoted ones.
• Jump to file by pressing F3 e.g. to open a HTML page referenced by a form action attribute. You can however do this in PDT by right clicking and choosing Open Selection.