[plt-scheme] Convention for alists?

Is there a commonly-accepted convention for the shape of an association
list?  I've seen both
    '((a . 3) (b . 4) (c . 5))
and
    '((a 3) (b 4) (c 5))
before.

Clearly, the R5RS primitives will work on both, as will assf from
etc.ss; it's just a question of how one extracts the values.

(Here's the context: my environment library, in PLaneT/300, exports an
env->alist function that returns a list of the second form above.
Should I change it to the first?)

Richard