I still drop into my DOS-BRIEF once in a while just for the sheer nostalgia of it :-)
I use EMACS now. The commands require more keystrokes but I have pretty much everything in it that BRIEF gave me. With the right amount of configuration, EMACS stays out of your way too.
If you loved working with BRIEF, I think you will like EMACS. There's something about the philosophy behind the two editors that appeals to me - the amount of thought that has gone into each feature, the customizability, the sheer power.
BRIEF stuff you will find in EMACS, and not in many other editors:
1. Column block cut/copy/paste
2. Filename completion / folder listing without opening a dialog / window
3. Intuitive navigation
4. Way more text manipulation stuff
5. In-editor compilation and debugging (although this is usually a bit more painful to get working right)
6. Split buffers
7. Buffer list
8. Get stuff done with the keyboard more, and depend on the mouse less
9. Powerful macros
10. Powerful regular-expression search / replace, speed search
11. Powerful scripting language with compilation
And a whole lot more...
You can even hide the scrollbars :-)
The one thing you will likely miss is Num-key minus and del keys for cut / delete, ins for paste. (If you use a notebook, this won't be a problem anyway since getting at these keys on a notebook would be way more difficult than EMACS' default key bindings). And you could configure EMACS key-bindings to handle this if you really want to. I've used scripting to get line mark/cut in a single operation like BRIEF and unlike EMACS' default behavior which is you mark the line with one command and then cut it with another.
One word of warning though. With BRIEF you could start being productive in a week. EMACS needs way lot more work than that but I've found it worth it.
The other key thing I like about EMACS is that it is available on pretty much every operating system out there. I use a MacBook with Mac OS X and Windows XP. I also occasionally use Ubuntu Linux. EMACS is available everywhere and I don't have to stop and think about anything when switching between these OS'.
Hope this helps.