i have used 222,17rem fireball,223,22/250 and seen 204 used to great affect to by my mate who has one. he also has a 6br which is very good.
what you have to look at is the shooting you do what sort of ground do you shoot over. around here there pretty large fields so most shots are around the 200 yards at night some even out to 250 depending on how lamp shy the fox is.
i love the 22/250 it hits very hard, its very forgiving at night under the lamp. by this I mean sometimes range can be hard to get right at night. and you haven't always got the chance to range it with rangefinder. the