Emacs in *nix world and Visual SlickEdit in Windows world.
Things I want:
Multiple documents and buffers that are easy to switch between are a must. Split screen is nice in a graphic environment. Multiple cut and paste buffers are nice as well.
Built in Diff is something I don't think I can do without anymore.
Access to compiler and debugger such as exist. SlickEdit is nice for this; it integrates with Visual Studio nicely, but doesn't insist on it if I just want to use the DDK. I can get to Visual Studio help and MS C symbols reference too. Getting to version control is also good.
Macros! On the fly or build your own. That's something else I don't know how I got along without.
Editing in hex mode is an awful nice feature.
I have use a lot of editors, but those have been mostly what I have used for the last 8 or 9 years.
Hugh