The free Idera PowerShellPlus remains my go to PowerShell editor for the unique combination of features it has...

I maintain a large PowerShell code library for my team.  If I am just fixing a quick script, the PowerShell ISE 3.0 is sufficient. However, if I'm in for several hours of code updates - then Idera has a handful of key features that make a big difference:

• "Search => Hitlist" functionality which shows a list of lines where your search term exists in the current file or all loaded files.  Given the shift in human expecations of "search capabilities" fostered by Google, it is utterly amazing to me that this feature is not yet "stock" on every PowerShell editor - actually every text editor.
• Supports PowerShell #Region tags for collapsing lesser used portions of code.
• Can run portably (from a folder without install - easy to replicate via cloud files)
• Supports VBS highlighting (32-bit Edition Only) - since you can't convert everything to VBS overnight!

Even though Idera made the product free, it has continued to advertise and improve it in small increments.  Version 5.0 has the following enhancements and changes:

• More compliant syntax highlighting engine allows better detection and display of language syntax and structure. (Native Intellisense)
• More compliant breakpoints for debugging - expands breakpoints to support "variable" and "command" breakpoints along with previous "line" breakpoints.
• Syntax highlighting for Desired State Configuration (DSC) scripts.

As of this release PowerShellPlus requires your machine to have PowerShell 3.0.  If you have to support PowerShell 2.0 with your scripts, it will be important to test on 2.0.  Much of the sample code on the web now reflects the 3.0 language - which means it can need adjustment to run under 2.0.

In regard to testing your code in all your target execution environments, our Mini-course "PowerShell for the Enteprise Desktop: Quick Tips, Tricks & Ready To Run Code" has one lesson that contains the code for configuring many shell extensions for .PS1 files.  It has options for every combination of "admin/non-admin", "32-bit/64-bit" and "Version 2 / Version Latest". Check it out at elearning.CSI-Windows.com