Here is a quick post about Best PHP IDE. PhpStorm and Sublime Text has won as best PHP IDE. PhpStorm is not free but Sublime Text is free. Both Sublime Text and PhpStorm are multi platform and supports many language. Both support many languages so developers who work on many languages may like both IDE.
So, people who use Notepad++ can try Sublime Text as this is also free and lightweight. PhpStorm is also lightweight and it uses modified IntelliJ IDEA. Therefore, for an IDE, it looks multi-platform, light weight, and support for multi languages (using plugins) are big advantages. I have some experience with Sublime Text on MacBook but not with PhpStorm.
PhpStorm is priced at $129 and upgrade from 2nd year at $49 for Personal use. One year upgrade is included in purchase license.
For me (India), PhpStorm looks costly. It is coming at Rs. 7855 for an year license and Rs. 2983 for upgrade at current rate of conversion (USD to INR).
There should be free lifetime upgrade for personal use. Agree?