I should mention that you really do want good editor support with any dialect of Lisp, because having to balance parentheses by hand gets old fast. You want an editor where you can have keybindings for "pull this space-delimited item out of the current parentheses and stick it into the parent set of parentheses" and all the other operations that are extremely common in Lisp. Also, smart auto-indenting is absolutely essential in order to produce readable Lisp code. You need things lined up correctly if you want to be able to read the code without resorting to counting closing parens. This is why so many people use Emacs, because it was designed for Lisp from the ground up. But I never liked its Ctrl+Shift+Meta+key shortcut methods, hence why I'm recommending Vim.

Emacs does have one advantage over Vim when it comes to Lisp, though, which is that it almost certainly comes with Lisp-related keybindings already ready to go. And also that its config files are written in Lisp, so if you're using Emacs then you're already reading and writing Lisp code just to configure it. Two. Two advantages. Oh, and fanatical devotion to the Pope ^W^W Richard Stallman. Three advantages... I'll come in again.