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I typically use Eclipse PDT.... I like it because:
there are versions for both Windows and Linux - so it's easy to switch between my various systems.easy to create/modify coding styles (modified PSRxx, etc)it's freeeasily "jump-to" referenced functionscustomized syntax highlighting for PHP, JS, XML, MySQL, etcrefactoringGitHub integration (easy to pull/push/commit/etc)Composer supportGood build/run toolsEclipse community supportBug/Issue tracking integrationcode completion
The one drawback is lack of Smarty syntax support - there's a plugin for it but it's old & doesn't work well.
I also use Notepad++ for a quick editor when needed. PHPStorm is a good product too but I haven't found enough difference/advantage to it that would cause me to change from Eclipse (and pay the money).