λ for short procedures (i.e., (λ (x) (+ x 1))), lambda for the rest:
(with-anus
(λ () ; too much wasted space
...1
...2))
(with-anus
(λ () ...1 ; too much indentation, looks ugly.
...2))
(with-anus
(lambda () ; ok for me.
...1
...2))lambda/λ, because it's more likely to use fn/fun/proc than λ as variable name.