Use what you've got, or anything really.
Not that it won't make a difference, but i will say that in terms of the end result it's not particularly sensitive to what you use in terms of it making that much difference ie it will still sound quite cool and vocoded but the nuance of your synth doesn;t really come through that much.
E.g this one was done with a Memotron using male and female choir sounds:
And this with a Waldorf Microwave XT:
if you don't have a synth i'd say pick something with maybe strings and pad sounds you like, but don't obsess over what you use for this purpose.