I use Alan Philip's "Programmer's File Editor", PFE on my Windows boxes. Here are my reasons for using this tool, rather than others.

• I've used it for over 5 years, so I'm familiar with it - though we all claim sound reasons for editor "x" or "y", I think familiarity is a big reason we all stick with our favourites
• It's free, though not open source. I don't have money to splash around, especially when I started to use it
• It's very small, 608kb, so it's easy to move around
• It's got a nice multi-document interface - though it's looking dated now
• It's quite flexible and configurable, has nice simple macros, good search/replace, and was designed to talk to an external compiler and caputure the results
• If you tell it Perl is c, then it does a nice job at auto-indenting your code for you, which is ofcource configurable
• It's very fast to start, and it's easy to live with
• It can save either with *nix or Windows line endings

I'm sure there are other nice things about it, but I think the list is long enough. It's a dead product, but until something better arrives, I'm sticking with it.

I think if I were to want features in a perfect editor, for a casual user like my self, I'd want:

• Small and fast
• I like the idea of syntax highlighting in colour, but I find it irritating over time (I have dyslexia), and don't use much
• Easy interface to the Perl complier
• Plug-in archtecture, HTML-Kit for example allows to you plug in the W3C HTML, XML and CSS specs, so you can have context sensitive help directly from the source - doing the same in Perl would be nice too!
• It's always nice if it's free and open source, but I will pay a few £s if it's really good.