declaring local variables inside functions?

[SaraFdS]

A simple(?) question that just came to my mind, when using local variables inside local functions, what's the most efficient and/or fastest way to do so?
Declare it once, outside the function

local foo = SomeValue
local function goo()
foo = SomeValue
-- do sth w/ foo
end

or declare it each time anew inside the function?

local function goo()
local foo = SomeValue
-- do sth w/ foo
end