I would go pastel het clown x pastel het clown if you want killerclowns.

If money wasn't an issue, I'd go with pastel clown female and pastel het clown male.. That way you have a pastel clown girl that can produce 100% het clown x pastel x whatever you pair her with.

I wouldn't do pastel clown x pastel clown because you would be spending so much more just to get slightly better odds on your crown jewel. However you would get 100% clowns in your clutch.