I have a smooth collie bitch 7 months old and want to get a border collie for ringcraft,obedience etc but unsure whether it would be best to get a male or female.What is the best combination,a boy and girl or two girls.

Generally speaking boy/girl is a safer bet. Bitches are usually all right together but if you are unlucky enough to get 2 bitches who don't get on, one usually has to be rehomed. Presumably you will have to get one neutered? If you want to do obedience a bitch is generally easier to train ( altho' I love dogs myself.)
Not much help am I?