Editing comfort
Emacs is on my long list of things that I love in theory, but in practice have only the most tenuous of grips on. (See also: Go, wine tasting, Fourier analysis. Also, I know I ended a sentence with a preposition. Suck it up.)
So – and I say this with all love and in spite of my new year’s resolution – Eclipse with Counterclockwise? So much easier to use than Emacs with SLIME. Almost certainly less powerful, but for the purposes of learning a language, I do not care.