Better to use "and" or "in" when chaining "let" statements?

I realize this is probably a silly question, but...

If I'm chaining a bunch of let statements which do not need to know each other's values, is it better to use and or in?

For example, which of these is preferable, if any:

let a = "foo"
and b = "bar"
and c = "baz"
in
  (* etc. *)

or

let a = "foo" in
let b = "bar" in
let c = "baz"
in
  (* etc. *)

My intuition tells me the former ought to be "better" (by a very petty definition of "better") because it creates the minimum number of scopes necessary, whereas the latter is a scope-within-a-scope-within-a-scope which the compiler/interpreter takes care to note but is ultimately unimportant and needlessly deep.