I would suggest a night rating before an IMC, purely because it is great fun and you actually need it and might want to use it.
This is a debate that comes up time after time, and the general concensus is
not to do it this way round.
Why?
1) There are more chances of flying in bad weather than there flying at night in the UK (with typical airfield availability / operating hours).
2) It's OK flying at night without an IMC - but you can't see clouds at night until it's too late (When you're inside them). What becomes the more important qualification then?